If you run a limited company, there is one small code that does a surprising amount of work. Your company authentication code lets you file information with Companies House online. That includes your annual accounts, your confirmation statement and changes to your directors or registered office. Without it, you cannot file online. And in the wrong hands, someone could use it to make changes to your company records.
This guide explains what the code is, where to find it, what to do if you lose it, and how to keep it safe. It is based on the official GOV.UK guidance on company authentication codes, written in plain English.
What is a company authentication code?
A company authentication code is a short code made up of letters and numbers. Companies House gives one to every company on its register. Each company has its own code.
When you file something online, Companies House treats the code as the company's signature. In other words, entering the code tells Companies House that the filing has been approved by the company. So anyone who has the code can, in practice, file information on the company's behalf.
Think of your authentication code as your company's signature for online filing. Treat it with the same care you would give a bank PIN.
What you use the code for
You need the code whenever you file information with Companies House through its online services. Common examples include:
- filing your company's annual accounts
- filing your confirmation statement, the yearly check that the information Companies House holds about your company is correct
- appointing or removing a director or company secretary
- updating an officer's details, such as a change of name or address
- changing your registered office address
If an accountant or other agent files for you, they will usually ask for your authentication code so they can do this.
Heads up - this code is from Companies House, not HMRC. It is not the same as your Unique Taxpayer Reference (UTR) for Corporation Tax, or the activation code HMRC sends when you sign up for its online services. It is easy to mix them up, so keep a note of which is which.
Where to find your code
Companies House sends the code to the company when it is set up. If the company was formed online, the code is usually provided as part of that process. Otherwise, it is sent by post to the company's registered office address.
If you have run the company for a while, check your records first. The code may be in the original incorporation paperwork, in a letter at your registered office, or held by your accountant.
What to do if you have lost your code
Losing your code is common and easy to fix. You can ask Companies House for a new one through its online services. Companies House will then post the code to your company's registered office address.
A few practical points to keep in mind:
- It goes to the registered office. Companies House sends it there for security reasons. So make sure someone can collect post from that address.
- It takes time to arrive. Because the code comes by post, it can take several working days. Do not leave this until the week your accounts or confirmation statement are due.
- Check your registered office is up to date. If the address on the register is old, the code will go to the wrong place.
Heads up - Companies House filing deadlines still apply even if you are waiting for a new code. If a deadline is close, request your code as early as you can so you avoid late filing penalties.
How to change your code
You can change your authentication code at any time using Companies House's online filing service. You will need your current code to do this.
It is a good idea to change it if:
- a director or employee who knew the code has left the company
- you have stopped using an accountant or agent who had the code
- you think someone may have seen or used the code without permission
Once you change it, the old code stops working. Remember to give the new one to anyone who still needs to file for you.
Keeping your code safe
Because the code acts as your company's signature, it is worth protecting. Here is what we suggest:
- only share it with people you trust and who genuinely need to file for the company
- store it somewhere secure, not on a sticky note or in an unprotected email
- change it whenever someone who knew it no longer works with you
- check your company record on the Companies House register from time to time, so you spot any changes you did not make
Companies House also offers a free email alert service. It can tell you when someone files information for your company, which helps you catch anything unexpected quickly.
Quick guide: which step fits your situation
| Your situation | What to do |
|---|---|
| You have just set up a company | Keep the code from your incorporation somewhere safe |
| You cannot find your code | Request a new one online; it is posted to your registered office |
| Your accountant files for you | Share the code with them securely |
| You have changed accountant | Change the code, then give it to your new accountant |
| A director has left | Consider changing the code if they knew it |
| You think the code has been misused | Change it straight away and check your company record |
| A filing deadline is close and you have no code | Request a new code as early as possible to allow for post |
How this fits with identity verification changes
Companies House is changing how people prove who they are. Under new company law reforms, directors and people who file information are being asked to verify their identity, and Companies House is moving to GOV.UK One Login for signing in to its services.
Over time, identity verification is expected to replace authentication codes for many filings. But the changes are being brought in gradually. For now, you should keep your authentication code safe and keep using it where Companies House asks for it. We recommend checking Companies House's latest guidance, or asking your accountant, so you know what applies to your company and when.
Final thoughts
Your company authentication code is small, but it matters. It is your company's signature for online filing, so keep it safe, share it only with people you trust, and change it when people move on. If you lose it, ask for a new one early, because it comes by post to your registered office.
Get this right and filing your accounts and confirmation statement becomes one less thing to worry about. And if you are unsure about anything, your accountant or Companies House can help.