Companies House Authentication Code: What It Is and How to Use It

Every UK limited company registered at Companies House is issued a six-character authentication code. This code functions as the password that authorises online filings on the Companies House WebFiling service. Without it, you cannot submit a confirmation statement, file annual accounts, or make director and address changes online. Understanding how it works — and what to do if you don't have it — is essential for any director managing their own compliance.

What the authentication code looks like: the code is exactly six characters, combining letters and numbers (for example, AB1CD2). It is case-sensitive and unique to your company. It is not related to your company number, UTR, or any other identifier. Companies House issues it automatically when a company is incorporated, and it is posted to the registered office address — not emailed, not displayed in any online portal.

Where to find it: the authentication code is sent by post to the registered office address at incorporation. If you use a professional registered office service (as many Arab directors do), your provider should have retained it or forwarded it. If you incorporated through an agent, they may hold it. It is not retrievable online — Companies House does not display it in any portal, even after you log in. If you cannot locate it, you must request a new one.

How to request a new authentication code: if you have lost or never received the code, you can request a replacement through Companies House WebFiling. Log in, navigate to 'Request an authentication code', and Companies House will post a new six-character code to your registered office address. The replacement takes up to five working days to arrive by post. There is no faster option — Companies House does not issue codes by email or phone as a security measure.

Why the registered office address matters: because the authentication code is sent by post to the registered office, having a reliable professional registered office address is not just about compliance — it is also about access. A director based in Dubai or Riyadh who uses their home address as the registered office will never receive Companies House post reliably. All official correspondence (including a replacement authentication code) will go to that address. A London professional registered office address ensures you actually receive it.

What happens if you file without the correct code: WebFiling will simply reject the filing. There is no alert to the regulator — you just cannot submit. If your filing deadline is approaching and you are waiting for a replacement code, contact Companies House directly (telephone or webchat) to explain the delay, and if needed request an extension in writing. Courts and Companies House can be sympathetic in genuine delay cases, though this is not guaranteed.

The authentication code and ACSP authorisation: one important nuance for 2026 — when Fileminder (as an Authorised Corporate Service Provider / ACSP) files on behalf of a client, it does so using the ACSP's own credentials, not the client's authentication code. This means an ACSP-authorised firm can file the confirmation statement and annual accounts without needing the director to provide the authentication code. For directors who have lost their code, using an ACSP removes the dependency on the postal delivery timeline.

Keeping the code secure: treat the authentication code like a password. Do not share it by WhatsApp or email unless it is with a trusted accountant. Anyone who has your code and company number can file changes with Companies House — including resigning your directors or changing your registered office. If you suspect the code has been compromised, request a new one immediately through WebFiling, which invalidates the old code.

In summary: the authentication code is a small but critical piece of your UK company compliance infrastructure. Know where yours is, keep it secure, and ensure your registered office address is reliable so you can always receive a replacement quickly if needed.