What is my Government Gateway user ID for Corporation Tax?

In short: It's the sign-in ID for the company's HMRC business tax account. GOV.UK describes Government Gateway as "a user ID (up to 12 characters) and password", so it isn't your email address (GOV.UK: HMRC online services). Use the ID that has the company's Corporation Tax added, and recover lost details from HMRC's sign-in page. Taxley files the CT600 with that user ID for £44.50 (promotion price until 31 Dec 2026; £89.00 from 1 Jan 2027) with micro-entity accounts, then files the accounts at Companies House once the return is paid and finished.

Take the 30-second check to see whether Taxley fits your company, or start your return.

Key facts (checked on 1 October 2026)

What is a Government Gateway user ID?

It's the ID HMRC gives you when you create Government Gateway sign-in details. With a password, it opens HMRC online services such as the company's business tax account. GOV.UK says it has up to 12 characters (GOV.UK: HMRC online services), and HMRC's One Login announcement calls it a 10 to 12 digit ID (HMRC: One Login for new customers).

You don't choose it. HMRC's filing protocol defines the user ID as "a unique alphanumeric string generated at registration (not selected by the user)" (HMRC: Transaction Engine Document Submission Protocol), and HMRC's registration help says it's shown on screen when you register, to note down and keep safe (HMRC: registration FAQs). For Corporation Tax, the right ID is the one that holds the company's business taxes: GOV.UK says you'll need the sign-in details you used when you first registered a business tax (GOV.UK: Sign in to your HMRC business tax account). HMRC's business tax account guide adds that a business should use one Government Gateway user ID for all its taxes, and that the account shows a tax card for each tax registered with that ID (HMRC: business tax account guide). No Corporation Tax card after you sign in means a different ID, or Corporation Tax not yet added.

Is my Government Gateway user ID my email address?

No. GOV.UK lists two ways to sign in to HMRC: Government Gateway, with "a user ID (up to 12 characters) and password", and GOV.UK One Login, with "an email address and password" (GOV.UK: HMRC online services). Software that asks for a Government Gateway user ID needs the ID itself, never an email address.

The mix-up is easy to make because directors now hold several sign-ins. Companies House WebFiling has needed GOV.UK One Login, which signs in with an email address, since 13 October 2025 (GOV.UK: Filing your Companies House information online). HMRC says a customer with a Government Gateway account keeps using it for HMRC, even if they have a One Login for another service such as Companies House (HMRC: One Login for new customers). Giving HMRC an email address when you registered doesn't make it your Gateway sign-in: the user ID is what you type. In Taxley's own live filings, an email address typed in place of the user ID is a frequent reason HMRC refuses the sign-in with error 1046. The guide to fixing a CT600 rejected with error 1046 covers that error and the other common causes.

Where can you find the company's Government Gateway user ID?

Start with the note made when the sign-in was created, because HMRC shows the user ID on screen at registration and asks you to keep it safe (HMRC: registration FAQs). Then check a password manager or browser, and ask whoever set up the company's HMRC account.

Taxley's checklist: where to look for the user ID

Look before you create anything new. HMRC's business tax account guide says to use only one Government Gateway user ID and not to create a new one, and that someone using more than one ID may be able to align their tax registrations to one ID (HMRC: business tax account guide). Once signed in, the same guide says you can view or change your account details, including your Government Gateway user ID, under manage account. A second ID starts without the company's Corporation Tax, so you'd have to add it again and wait for an activation code by post: the Corporation Tax activation code guide sets out those steps and how long they take. Don't confuse the user ID with the company's Unique Taxpayer Reference (UTR), the 10-digit number on HMRC's letters (GOV.UK: Find your UTR number). Filing software needs both, but for different jobs: the UTR identifies the company, and the user ID and password authorise the submission.

What if you've lost the user ID or password?

Use the recovery route on HMRC's sign-in page. GOV.UK says you can recover or reset lost sign-in details, and that you'll be told how to do this when you try to sign in (GOV.UK: problems signing in). HMRC may ask questions to confirm your identity before it lets you back in.

HMRC's guidance on keeping sign-in details safe says identity checks are also used for security processes, for example if you have forgotten your sign-in details (GOV.UK: Keeping your HMRC sign in details safe). If the problem is the access code rather than the user ID, GOV.UK says the code can come by text message, voice call or authenticator app, and that you can change the method by signing in and selecting "You can get help" when asked for the code. Guessing has a cost: you'll be locked out after entering the wrong sign-in details too many times, the account unlocks after 2 hours, and helpdesk advisers can't unlock it (GOV.UK: problems signing in). HMRC's digital assistant can help with online services, and can pass you to a webchat with an adviser when one is available. Leave enough time before the filing deadline: if recovery fails and you need a new ID with Corporation Tax added, HMRC posts the activation code within 10 days, or 21 days if you live abroad (GOV.UK: Add Corporation Tax services).

Which sign-in should a company use, and which should an accountant use?

A company filing its own CT600 uses its own Government Gateway user ID with Corporation Tax added. An accountant files with the practice's own agent sign-in and the company's authorisation. GOV.UK says you must not share your HMRC sign-in details with anyone, including your tax agent (GOV.UK: Keeping your HMRC sign in details safe).

Taxley's decision table: which sign-in files the CT600

GOV.UK's guidance on agent authorisation says the same from both sides: you must not give your sign-in credentials to your agent, and an agent must not use a client's credentials to sign in to any account (GOV.UK: Change or remove your tax agent's authorisation). Tax advisers who must register with HMRC do so through an agent services account, which gives access to Corporation Tax among other taxes (GOV.UK: Client authorisation overview). Using an agent doesn't lock the company out of its own account: HMRC's business tax account guide says a business that uses an agent can still use the business tax account to check what's happening (HMRC: business tax account guide). A director who files Self Assessment often has a personal sign-in as well, so check which ID shows the company's Corporation Tax card before filing. Adding Corporation Tax to the right ID, and activating it, is covered in the Corporation Tax activation code guide.

Can you use GOV.UK One Login instead of the Government Gateway user ID?

Not for filing a CT600: continue using Government Gateway for CT600 software filing. HMRC's current One Login rollout covers personal tax services (GOV.UK: HMRC online services): it began offering One Login to new individual customers on 9 February 2026 (HMRC: One Login for new customers).

HMRC's guidance on One Login says it will, over time, replace all other sign-in routes, including Government Gateway, and that you don't need to do anything differently until HMRC prompts you (GOV.UK: Accessing HMRC online services using GOV.UK One Login). When you sign in to HMRC, you can choose Government Gateway, GOV.UK One Login or "Create new sign in details". When HMRC asks you to move, you may need to go through a new identity check, with documents such as a passport or driving licence. A One Login you already use for Companies House doesn't change this: HMRC says existing customers must keep using their Government Gateway for HMRC for now (HMRC: One Login for new customers). Online CT600 filing still uses a user ID and password: HMRC's filing protocol authenticates each submission with the sender's user ID and password (HMRC: Transaction Engine protocol).

How does Taxley use the company's Government Gateway user ID?

Taxley (taxley.co.uk), UK online software that prepares and files the Company Tax Return (CT600) with HMRC and the annual accounts with Companies House, asks for the company's own Government Gateway user ID and password when you file, and sends them to HMRC with the return, as HMRC's filing protocol requires (HMRC: Transaction Engine protocol).

Taxley never saves the password to your account or filing. It is held encrypted while sending; if sending fails, the encrypted record is deleted within three days. It's blanked out of the copy of the submission Taxley keeps. The user ID stays in that copy, encrypted. Before anything reaches HMRC, Taxley removes spaces from the user ID and refuses anything that looks like an email address. A short checklist above the sign-in boxes asks you to check that the details work on GOV.UK and that this company's Corporation Tax is listed there. An accountant using Taxley's agent mode enters the practice's own HMRC agent sign-in instead. The filing form has no GOV.UK One Login option. A "Run a test" rehearsal uses Taxley's own test sign-in and HMRC's test reference, so it doesn't check your details; signing in on GOV.UK does. Take the 30-second check to see whether Taxley fits your company.

Frequently asked questions

How many characters is a Government Gateway user ID?

GOV.UK says up to 12 characters (GOV.UK: HMRC online services), and HMRC's One Login announcement calls it a 10 to 12 digit ID. HMRC generates it as a string of letters and numbers, so it never contains an @ sign.

Is the Government Gateway user ID the same as the company's UTR?

No. The UTR is the company's 10-digit tax reference on HMRC's letters (GOV.UK: Find your UTR number). The user ID is a sign-in name for HMRC online services. Filing needs both: the UTR identifies the company, and the user ID authorises the submission.

Can two directors share the company's sign-in?

HMRC's business tax account guide says account administrators can give team members access to manage business taxes (HMRC: business tax account guide). Use that rather than passing the password around, and keep one Government Gateway user ID for the business.

Should I create a new user ID if I can't find mine?

Only as a last resort. HMRC's guide says to use one Government Gateway user ID for the business and not to create a new one (HMRC: business tax account guide). A new ID needs Corporation Tax added again, with an activation code by post.

Does a Taxley test run check my Government Gateway sign-in?

No. A "Run a test" rehearsal sends the return to HMRC's test service with Taxley's own test sign-in and HMRC's test reference, so it checks the return, not your details. To check the sign-in, sign in to the company's business tax account on GOV.UK.

General information, not personalised tax advice. Sign-in rules checked on GOV.UK on 1 October 2026; HMRC is moving customers to GOV.UK One Login in stages.