It has been an issue for many years that you cannot download an SA302 form from HMRC when the tax return is filed using commercial software and so it means a telephone call to HMRC to obtain a copy by post. HMRC have approved the tax calculation produced from approved commercial software as a SA302 substitute for many years but lenders generally don’t accept these.
HMRC have recently updated tax agents with this information below and it is worth following up with your lender and quoting this if you are having issues with proof of income
We know you and your clients may have concerns around the delay in issuing SA302 tax calculations/evidence of earnings where they’re needed for mortgage applications. We have written to mortgage lenders to update them on the situation and ask that they consider accepting alternative evidence until this is resolved.