The Submission section takes the return from prepared to filed: pre-flight checks, the declaration, the submission itself, and a history of every attempt.
Pre-flight checks
Every check must pass before the Submit button unlocks, and every one is re-verified on the server at the moment of filing:
- the year is open for submission (not already accepted, unless amending)
- the client has a valid UTR on their record (it is checked against HMRC’s check-digit algorithm, not just for presence)
- a National Insurance number is entered in Personal Details
- calculation support exists for the tax year
- there are no blocking calculation warnings
- where the return has a Capital Gains page, the computation summary is entered in its box 54 — HMRC rejects an SA108 without one
- a Government Gateway login is saved for the SA100 (see below)
Anything failing shows in red with what to fix. Where the fix is on another section of the return, a Go to link beside the check takes you straight there; come back to Submission afterwards and the list is checked again, or press Re-check to run it at any time.
The Government Gateway login for the SA100
HMRC only accepts an SA100 from a Government Gateway account that is allowed to file Self Assessment for that person, so the return is sent with a login. Tax Optimiser uses, in this order:
- The client’s own login, when you have saved one in the Government Gateway login for the SA100 box on the Submission section. Use this only for a client who files under their own Government Gateway account.
- Your firm’s agent Self Assessment login, saved once under your firm’s settings, HMRC tab (Self Assessment Sender Id and Self Assessment Password). This is the usual choice: it covers every client you are authorised to act for, and nothing needs saving against the individual.
The box tells you which login the return will go out under. Logins are stored encrypted and a saved password is never shown again — leave it blank to keep it, type a new one to replace it, or use Remove saved login to delete it.
This login is for the SA100 only. Making Tax Digital for Income Tax does not use it — MTD connects through HMRC’s own sign-in — which is why the box appears here and nowhere on the Making Tax Digital screens. Do not save a Government Gateway password for a client who only uses Making Tax Digital.
Declaration and submit
Tick the declaration — the standard Self Assessment wording that the return is correct and complete to the best of the taxpayer’s knowledge — and press Submit to HMRC. Tax Optimiser builds the return in HMRC’s required format, signs it with the tamper-evident IRmark, sends it, and polls HMRC for the response, all in one step. The section shows a progress panel while this happens — it can take a minute — and then the outcome: Return accepted by HMRC, or the problem HMRC reported. On success the year moves to Accepted and locks against accidental edits; if HMRC rejects the return, their errors are shown in full and the year reopens for correction as soon as you edit it.
The submission history
Every attempt is recorded with its date, status (Waiting for HMRC, Accepted or Rejected), whether it was an amended return, and its HMRC correlation ID — the reference to quote if you ever need to speak to HMRC (or to support@taxoptimiser.co.uk) about a filing. If a submission is still showing Waiting for HMRC — for example after a connection drop mid-poll — the Re-poll button asks HMRC for the outcome again without resubmitting anything. Tax Optimiser also chases stuck submissions automatically in the background every fifteen minutes, so a return interrupted mid-poll usually resolves itself without any action from you.
Next: Amending an accepted return.