If you own or manage a UK limited company, you may eventually be asked for a Companies House authentication code when filing information online. The code is an important security credential that helps Companies House confirm that someone is authorised to make online filings for a company. It is particularly relevant when changing company details, filing certain information through WebFiling or managing statutory records online.

For founders who have recently incorporated a company, the authentication code can seem confusing because it is different from a company number, a WebFiling password and the newer Companies House personal code used for identity verification. Understanding the difference matters. Losing the authentication code can make certain online filings more difficult, while sharing it carelessly can create a security risk.

What Is a Companies House Authentication Code?

A Companies House authentication code is a unique code associated with a UK company that is used to authenticate online filings and changes made through Companies House services. It effectively acts as a company's online filing password. Companies House guidance confirms that the authentication code is required when using its WebFiling service to make certain changes to a limited company.

The code belongs to the company, rather than being the personal identity-verification code of a director. That distinction has become increasingly important since Companies House introduced mandatory identity verification for directors and Persons with Significant Control (PSCs).

What Is the Companies House Authentication Code Used For?

The authentication code is used to prove that someone submitting certain information online has authority to file information for the company. For example, Companies House says you need the authentication code when using its online service to report changes such as:

• A change of registered office
• A change of company name
• Changes involving directors or company secretaries
• Changes to PSC information
• Changes to share structure
• Certain mortgage or charge information
• Other company filings

It can therefore become particularly important when your company is being actively managed.

Example

Imagine that Brightway Consulting Ltd moves from one registered office to another. Someone authorised to make the change online may need:

1. The company's Companies House account details
2. The company's authentication code
3. Other information required for the particular filing

The authentication code helps Companies House establish that the person making the online filing has the necessary company-level authority.

Is the Authentication Code the Same as the Company Number?

No. These are two completely different things.

Company number

The company number is the unique identifier assigned to the company when it is incorporated. It identifies the legal entity.

Authentication code

The authentication code is a security credential used for certain online filing activities. Think of it this way:

Company number = identifies the company.
Authentication code = helps authenticate online filings for the company.

For example:

Company: Brightway Consulting Ltd
Company number: 12345678
Authentication code: A confidential security credential

The company number is routinely used when searching the Companies House register. The authentication code should be treated as confidential.

Is the Authentication Code the Same as a Companies House Personal Code?

No, and this is especially important under the UK's newer identity-verification system. Companies House now uses personal codes as part of identity verification for directors and PSCs. From 18 November 2025, identity verification became a legal requirement, with a 12-month transition period for directors and PSCs to complete verification according to their individual deadlines. The two codes serve different purposes.

A director can therefore have a personal code while the company itself has a separate authentication code.

Why the distinction matters

Suppose you are the sole director of a newly incorporated company. You may have:

• A company number
• A Companies House authentication code
• A personal Companies House code
• A Companies House account login

These are not interchangeable.

How Do You Get a Companies House Authentication Code?

When you register for Companies House WebFiling, Companies House sends the authentication code to the company's registered office address. Companies House states that if you have not used the service before, you can register online by providing your email address and creating a password. The authentication code is then posted to the company's registered office. This physical-mail process is an important security feature. It also means that companies need to maintain control over their registered office arrangements.

For a newly formed company

After incorporating your company, make sure you have a reliable system for receiving official correspondence. If you use a formation agent, accountant or registered-office service, establish clearly:

• Who receives Companies House correspondence
• Who scans or forwards it
• Who stores important credentials
• Who is authorised to file on your behalf

This can prevent a surprisingly common administrative problem: the company exists, but nobody knows where its authentication code was sent.

Where Is the Authentication Code Sent?

The authentication code is normally posted to the company's registered office. This is different from ordinary email-based passwords. The registered office is the official address of the company, and Companies House requires certain statutory communications to be sent there.

If your registered office changes, Companies House needs to be notified. Companies House says that a registered-office change must be reported and that the authentication code may be needed for the online filing. For businesses operated by founders overseas, this deserves particular attention. If you establish a UK company while living outside the UK, you need a reliable arrangement for handling official correspondence sent to the company's UK registered office.

What If You Lose Your Companies House Authentication Code?

Losing the code does not mean your company is lost or that you need to create a new company. You can request a replacement authentication code through Companies House. If you cannot access the company's registered office, Companies House also provides a process for requesting the code to be sent to a director's home address in certain circumstances.

The important point is not to guess, reuse or substitute another password. If you cannot find the code, use the official Companies House process to obtain a replacement.

Can an Accountant or Company Formation Agent Use Your Authentication Code?

Potentially, yes, if you have authorised them to handle filings for your company. Accountants, solicitors and company formation professionals can undertake Companies House filing work on behalf of clients.

The regulatory framework has also changed with the introduction of Authorised Corporate Service Providers (ACSPs). These are professionals authorised to provide certain Companies House services, including identity verification and filing activities. However, that does not mean you should casually send your authentication code to anyone who asks.

A sensible approach

If you work with an accountant or formation provider:

1. Confirm exactly what filing they are handling.
2. Confirm that you have authorised them to act.
3. Use a trusted professional.
4. Avoid sharing credentials through insecure channels.
5. Keep a record of who has access.

For a business owner using a UK company formation and management platform such as IncorpUK, it is sensible to understand which filings the platform handles and which credentials remain under the company's control.

Should You Share Your Companies House Authentication Code?

Treat it as confidential company security information. There may be legitimate circumstances where an authorised professional needs access to it to complete a filing for you. But you should never treat the authentication code like a public company number.

Companies House itself warns about scams in which fraudsters impersonate Companies House and attempt to obtain sensitive information, including authentication codes. Companies House says it will not call you asking for secure information such as an authentication code, password or bank details.

A useful rule

Company number: share freely when appropriate. Authentication code: protect it. That simple distinction can prevent unnecessary security problems.

What Happens If Someone Gets Your Authentication Code?

The authentication code is designed to help authenticate online filings, so unauthorised access could create a risk of improper changes being submitted. For example, someone with inappropriate access could potentially attempt to make changes to company information through online filing services. This is why Companies House authentication credentials should be handled carefully.

The importance of protecting the code was highlighted by a Companies House WebFiling security incident in March 2026. Companies House reported that a security issue potentially allowed a logged-in WebFiling user with an authorised code to access or change certain elements of another company's details after performing specific actions. Companies House closed WebFiling temporarily while it investigated and resolved the issue. That incident reinforces a broader point: company filing credentials should be treated as sensitive information.

Authentication Code vs Companies House Login

Another common source of confusion is the difference between your WebFiling login and the authentication code. Your Companies House account can involve:

• Email address
• Password
• Authentication code
• Company details
• Other security or identity-verification information

Your password identifies and authenticates your user account. The authentication code helps authenticate filings for the company. They serve related but different purposes. Losing your email password does not necessarily mean you have lost your company authentication code, and having the authentication code does not replace your account password.

Do You Need the Authentication Code to Run a UK Company?

Not necessarily for every aspect of running the business. You can operate many aspects of a company without manually using the authentication code every day. However, it becomes important when dealing with certain Companies House online filings. For example, if you need to update company information through WebFiling, you may need it.

Companies House has also introduced identity verification requirements, meaning directors and PSCs now have separate obligations involving their personal Companies House codes. Therefore, company owners should keep track of both: Company-level filing credentials and Individual identity-verification credentials.

What Is a Companies House Personal Code?

Because the terminology is changing, it is worth understanding the newer personal code separately. Companies House identity verification requires directors and PSCs to verify their identities. After successful verification, Companies House provides the individual with a unique personal code.

The personal code is used to connect the individual's verified identity with their company role. For directors, Companies House says the personal code must be provided as part of the company's next confirmation statement, while new directors will need to provide it as part of the registration process. This is one of the most important recent changes for UK company owners.

Why the Authentication Code Matters for Overseas Founders

The authentication code can be especially relevant to entrepreneurs who live outside the UK. A founder in Nigeria, India, the UAE, the United States or elsewhere may own a UK company without living in Britain. That can make administrative control more complicated. or example, the founder might:

• Live abroad
• Have a UK registered office
• Use an accountant
• Use a company formation provider
• Operate the business remotely
• Need to submit Companies House filings online

A clear process for receiving official correspondence and managing filing credentials is therefore essential. The authentication code should not simply disappear into an agent's inbox with no record of who controls it.

How to Keep Your Authentication Code Secure

A few simple practices can make a significant difference.

1. Store it securely

Keep a record in an appropriate password manager or secure company document system.

2. Don't publish it

Never place it on your website, social media, public documents or other publicly accessible location.

3. Be careful with email requests

Scammers may impersonate Companies House or professional service providers.

4. Verify professional requests

If your accountant or company formation provider asks for information, confirm why they need it and what they will be filing.

5. Maintain control when changing service providers

If you change accountants or company formation providers, make sure you understand who still has access to company credentials.

6. Keep your registered office information current

Important Companies House communications can be sent to the registered office.

Authentication Codes and Companies House Identity Verification: The Bigger Picture

The authentication code is part of an older system designed around securing company-level online filings. The UK's company-registration framework is now evolving. Under reforms introduced through the Economic Crime and Corporate Transparency Act 2023, Companies House has gained enhanced responsibilities and powers, including identity verification for individuals involved in companies.

From November 2025, identity verification began becoming mandatory for directors and PSCs, with implementation being phased over a 12-month transition period. This means company owners increasingly need to understand two separate concepts:

Company authentication — proving authority to file for the company.

Individual identity verification — proving that a person is genuinely the individual connected to a company role. They complement one another rather than replace one another.

Frequently Asked Questions

Is a Companies House authentication code the same as a company number?

No. The company number identifies the legal company. The authentication code is a security credential used for certain online company filings.

Where does Companies House send the authentication code?

It is normally posted to the company's registered office address.

Can I request a new Companies House authentication code?

Yes. If you have lost or cannot access your existing code, Companies House provides a process for obtaining a replacement.

Is the authentication code confidential?

Yes. It should be treated as sensitive company security information. Do not publish it or provide it to people you do not trust.

Can my accountant use my authentication code?

An accountant or other authorised professional may handle Companies House filings for you, but you should only provide access when you understand what they are doing and have authorised them to act.

Is the authentication code the same as my Companies House personal code?

No. The authentication code is associated with the company and online filings. The personal code is issued to an individual following Companies House identity verification.

Do directors need a personal code as well as the company's authentication code?

They can. The two codes perform different functions. Directors and PSCs are subject to Companies House identity-verification requirements, while the company may also have an authentication code for online filings.

What should I do if someone claiming to be Companies House asks for my authentication code?

Do not provide it until you have independently verified the request. Companies House warns that scammers impersonate the organisation and attempt to obtain authentication codes and other sensitive information.

Can an overseas company owner have a Companies House authentication code?

Yes. A UK company can have overseas directors or owners, subject to applicable UK company-law requirements. The authentication code remains associated with the company rather than the founder's country of residence.

Conclusion

A Companies House authentication code is a company-level security credential used to authenticate certain online filings. It is not the same as your company number, WebFiling password or personal Companies House identity-verification code. For company owners, the practical rules are simple:

• Know where your authentication code is.
• Keep it secure.
• Understand who has access to it.
• Do not confuse it with your personal verification code.
• Be cautious of anyone unexpectedly asking for it.
• Keep your registered office and company records up to date.

For founders managing a UK company from overseas, having a reliable system for handling Companies House correspondence and filings is particularly important. The authentication code may look like a small administrative detail, but it plays an important role in protecting the integrity of a company's online filings. As Companies House continues strengthening identity and filing controls, understanding the difference between company credentials and personal identity credentials will become increasingly important for anyone setting up or managing a UK company.