It is the HMRC Tax Calculation summary of an individual’s Total income and Income tax due. For anyone completing a Self Assessment form it’s their confirmation of Income from all sources in the same way as a P60 is a proof of Income from an employer.
When a tax return is submitted to HMRC online it is given a IR Mark which is unique to that tax return. This unique IR Mark is also listed as the Document IR Mark on the HMRC online filing log. It’s a security feature. If for any reason anything, no matter how small is changed on the tax return this IR Mark changed. So it is impossible to supply a SA302 with the same IR Mark as the HMRC online filing log which has been changed from the original tax return which was submitted to HMRC.
So why do Banks, Mortgage lenders, other Government departments insist the SA302 is only supplied by HMRC? As an Accountant, I have my own software and can produce clients SA302′s with HMRC online filing log, with matching IR Mark, which confirms it was the version submitted to HMRC. But instead I am told that HMRC online filing log, with matching IR Mark is not acceptable, but instead to contact HMRC to supply it. I’ll let you decide what you think.