Enrol for HMRC Corporation Tax Online (Government Gateway)

Before you can submit a CT600 to HMRC through TinyTax — or through any software, or via HMRC's own website — your company must be enrolled for Corporation Tax on a Government Gateway account. This is a one-time setup HMRC requires for every limited company. This guide walks you through it from a standing start.

When You Need This

You need to enrol for Corporation Tax if any of these apply:

• You're filing your first CT600 for a newly-incorporated company.
• Your CT600 submission keeps failing with HMRC Error 1046 (Authentication Failure) — see Fix HMRC Error 1046 for the diagnosis.
• You sign into your Business Tax Account and Corporation Tax doesn't appear in the list of services.
• You're a new accountant or filer for a company and the previous filer used a different Gateway account.

If Corporation Tax is already listed under your services in the Business Tax Account, you're already enrolled and don't need this guide.

What You'll Need

• Your Government Gateway User ID — the 12-character ID HMRC issued when you registered the Gateway account (a mix of letters and numbers; not the all-numeric account number you see on the home page).
• Your Government Gateway password.
• The 10-digit Company UTR (Unique Taxpayer Reference) HMRC sent in a letter shortly after your company was incorporated. If you've lost it, you can request a copy from HMRC.
• Your company's registered office address — HMRC will post the activation code there, so make sure you (or someone you trust) can collect post from that address.

Step-by-Step: Enrol for Corporation Tax

1. Sign into your Business Tax Account

Go to Government Gateway sign-in and sign in with the User ID and password for the Government Gateway account you want to use for filing.

If you don't have a Government Gateway account yet, create one first — choose Organisation as the account type (not Individual or Agent), since you're filing for a company.

2. Add Corporation Tax as a service

Once signed in:

1. Look for "Add a tax, duty or scheme" — usually on the Business Tax Account home page or under Manage account → Add a tax.
2. Select Corporation Tax from the list.
3. Enter your 10-digit Company UTR.
4. Confirm the company details HMRC shows match your company.

HMRC will tell you the activation code is on its way.

"This information does not exist for Corporation Tax, or it has already been used to request access to this tax or scheme"

This is the error HMRC shows at step 2 when it will not let you add Corporation Tax at all — you never get as far as being told an activation code is coming. It is one of HMRC's least helpful messages, because the single sentence covers two completely different situations.

What it actually means

Read the message as two separate statements joined by "or":

1. "This information does not exist for Corporation Tax" — the details you typed do not match a Corporation Tax record HMRC holds. Usually a UTR digit out of place, the wrong UTR entirely (a personal Self Assessment UTR rather than the company's), or a registered-office postcode that has since changed.
2. "...or it has already been used to request access" — the details are right, but an enrolment for that UTR already exists or is already pending on some Gateway account. HMRC ties the request to whichever record got there first, so a fresh attempt on a new account is refused rather than granted.

The second cause catches people out on a company's very first return, because it does not require anyone to have filed anything. HMRC often creates a Corporation Tax record automatically when Companies House notifies them of incorporation, and an enrolment may have been requested — by you months ago and forgotten, by a previous or prospective accountant, or by an agent acting for a former director — without a single CT600 ever being submitted.

Work through it in this order

1. Check the details against your HMRC letter, not from memory. Compare the 10-digit UTR digit by digit with an HMRC letter for the company (the "Notice to deliver a Company Tax Return", CT603, or a payment reminder). A personal UTR will never work here.
2. Try the previous registered-office postcode if the company has moved. HMRC may still be matching on the older address.
3. Go back through every Gateway account you already have and look for a Corporation Tax tile marked "pending activation". This is different from Corporation Tax simply not appearing in the list. If you find one, the enrolment was already requested on that account and you can request a re-issue of the activation code from that same screen — that is a much shorter route than starting over.
4. If nothing is pending anywhere, only HMRC can see where the request sits. Call the Corporation Tax helpline on 0300 200 3410 with the company UTR and company number to hand. The question to ask is specific: which Government Gateway account currently holds the Corporation Tax enrolment or pending request for this UTR, and can it be released or the activation code reissued? A general "I cannot file" will send you round the same loop.

If your filing deadline is close

Be realistic about the timing: even once HMRC identifies the account, an activation code still arrives by post and still takes 7-10 working days. If your deadline is days away, you are very unlikely to file in time, and the useful thing to do is protect your position rather than keep retrying.

HMRC can cancel a late filing penalty where you have a reasonable excuse — something that stopped you filing despite taking reasonable care. Being unable to enrol because of an HMRC-side record you cannot see or clear is the kind of circumstance that gets put forward, though whether it is accepted is always HMRC's decision. What helps is evidence gathered at the time rather than written up afterwards:

• Screenshots of the error message showing the date and time.
• A note of each Gateway account you tried and what happened on each.
• The dates and times of your filing attempts, and of any call to HMRC.
• Evidence of HMRC's own availability if their lines were closed when you tried.

If you have attempted CT600 submissions through TinyTax, contact support and we can confirm the dates, times and HMRC responses of those attempts in writing for you to attach to an appeal.

3. Wait for the activation code in the post

HMRC will post an activation code to your company's registered office address — not the address on your Gateway account, not your home address. The code is on a letter that looks similar to other HMRC correspondence, so check post carefully.

• Typical wait: 7 working days.
• Maximum wait: 10 working days. If nothing arrives by day 10, sign back in and check whether the request was actually placed (sometimes the form doesn't fully submit). If it was, request a re-issue from the same screen.
• HMRC cannot send the code by email, text, or to a different address. There is no way to speed this up.

4. Activate the service

When the code arrives:

1. Sign back into your Business Tax Account at Government Gateway sign-in.
2. Find the Corporation Tax tile (it'll show as "pending activation" until you do this step).
3. Enter the activation code from the letter.

Once activated, Corporation Tax stays enrolled forever on that Gateway account for that company — you only do this once. Future CT600 submissions through TinyTax (or anywhere else) will authenticate against this enrolment automatically.

Filing a CT600 Through TinyTax After Enrolment

Once activation is complete, return to your TinyTax dashboard and submit your CT600. On the credentials screen:

• Government Gateway User ID: the 12-character mixed-letters-and-numbers ID (not the numeric account number).
• Government Gateway password: the password for that account.
• UTR: the same 10-digit Company UTR you enrolled with.

If you still see Error 1046 after a confirmed-enrolled account, work through Fix HMRC Error 1046 to rule out the other two causes (wrong credential type, or temporary HMRC lockout).

Common Questions

Can I file before the activation code arrives?

No. CT600 submission to HMRC requires the Corporation Tax service to be active on your Gateway, not just requested. Any submission attempt before activation will fail with Error 1046. If your filing deadline is close, the activation wait is unavoidable — request it as early as you can.

My company was incorporated weeks ago and I haven't received a UTR. What do I do?

Companies House notifies HMRC on incorporation, and HMRC posts the UTR to the registered office automatically — usually within 14 days. If 4 weeks have passed and no UTR, request a copy or call HMRC on 0300 200 3410.

I've already filed via HMRC's free software / a previous accountant — do I still need to enrol?

If those filings worked, Corporation Tax is already enrolled — but possibly on a different Gateway account. Sign into the Gateway account you used previously and check that CT appears in the services list. If it does, that's the account to use in TinyTax. If you no longer have access to that account, you can recover it via the Gateway sign-in page; or you can enrol on a new Gateway and HMRC will treat the new enrolment as canonical going forward.

Can my accountant enrol on my behalf?

An accountant can file as an Agent with their own Agent Services Account, but TinyTax expects the company's own Government Gateway credentials (Organisation account type). If you're using an accountant to file via TinyTax, share the company's Gateway credentials with them — don't use the accountant's Agent account.

What if I'm a Charitable Incorporated Organisation (CIO), Community Interest Company (CIC), or other non-standard entity?

The Gateway enrolment process is the same regardless of company type. CIOs in particular often hit a snag because Companies House doesn't always pre-notify HMRC for charitable entities — you may need to register the charity with HMRC first. See Charities and community benefit societies for the wider context.

I missed the activation code letter and binned it — can HMRC re-send?

Yes. Sign in to your Business Tax Account, find the Corporation Tax tile (it'll still show "pending activation"), and request a re-issue from there. Allow another 7 working days for the new code to arrive.

The activation code expired — what now?

Activation codes are valid for 28 days. If yours expired, request a re-issue using the same process as a missed code. Don't try to use an expired code — it'll fail and you'll need to start the wait over.