Compliance & ECCTA
An authentication code that is rejected online is usually mistyped, expired after a reissue, or simply forgotten.
Written and reviewed by Waqas Sagar Member of ICAEW, Fellow of ACCA, Fellow of AAT, a double graduate and entrepreneur at heart, helping startups grow and serving thousands of businesses nationwide with an excellent team. Published by LimitedCompany.Accountants, 12 London Road, Morden, London SM4 5BQ. Reviewed 12 September 2026 against 2026/27 UK rates and current Companies House and HMRC guidance.
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QuickBooks PartnerCertified ProAdvisor100+ yearsCombined team experienceFully insuredUp to £2m indemnityRequest a replacement authentication code from Companies House online, which posts a new one to the company's registered office within a few days. There is no way to retrieve a lost code by phone or email for security reasons, so a reissue by post is the only route.
Why it stops working
How to get a working code
Request a replacement authentication code from Companies House online, which posts a new one to the company's registered office within a few days. There is no way to retrieve a lost code by phone or email for security reasons, so a reissue by post is the only route.
The authentication code is the company's own six-character password for filing online, separate from any individual director's personal verification code. It commonly fails because it has been mistyped, because someone previously requested a replacement and the old one no longer works, or because it was never passed on when a director or accountant changed.
It is not linked to identity verification and does not expire on a schedule, so if a correctly typed code is rejected the most likely explanation is that a newer code has already superseded it.
Apply for a new authentication code through the Companies House online service using the company number; it is posted to the company's registered office address, which is why keeping that address current and monitored matters even for companies with an appropriate address arrangement in place.
Once the letter arrives, update the code wherever your filings are prepared, including with your accountant or company secretarial provider if they file on your behalf, since an outdated code held by an agent will fail in exactly the same way.
Rates, thresholds and deadlines quoted here reflect the 2026/27 UK position and current Companies House and HMRC guidance. Check GOV.UK, or ask us, before relying on them for your own company.
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We work with company directors across London and Surrey from our office at 12 London Road, Morden, London SM4 5BQ. Pick your area, or send the form below and we will call you back.
Frequently asked
It is sent by post to the registered office, so allow for normal postal delivery time rather than expecting an instant code.
No, Companies House sends it only by post to the registered office for security reasons.
An ACSP acting for the company can usually help manage this, but the code itself still goes to the registered office by post.
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No. This page explains general UK rules and common accounting treatment. Your facts, contracts and wider tax position must be reviewed before you rely on a conclusion.
Included approach
Check the current rules
Deadlines, thresholds and filing rules change. GOV.UK and Companies House publish the current statutory position; advice should then be applied to your company’s circumstances.
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