I have evidence that once upon a time HMRC also knew that postcode to be correct.
HMRC have managed to change the postcode (how does this happen?) without any intervention from me.
Now the helpline for this type of return is only open mon-fri 9-5 (long story about a day spent on the telephone talking to 5 departments getting to the bottom of this problem omitted).
Even if I do get through on Monday morning it takes 3 days for them to update the system such that I can enrol for self assessment. Even with a following wind it is unlikely that I will then receive the activation code in time to actually submit the form by Jan 31. Guess who then has to pay a fine (tip, it's not them).
So .... either I need somebody to grant me an extension (good luck) or somebody who can tell me what the wrong postcode they have is so that I can use that to enrol instead ... I know it's a long shot, but thought I would ask - there must be some lurking HMRC or HMRC-spouse types on here

Cheers,
Robin