As you are in the "Self Assessment Club", you will report the move on the Self Assessment for the tax year of departure.
P85s don't have any deadline attached to them and are, at best, an indication of your date of leaving and whatever your intentions were at the time. Your circumstances may change, and you are not bound by anything you said in good faith when the P85 was submitted.
P85s are usually for someone leaving who never been in the habit of doing Self Assessments, or who wishes to make a tax refund claim (usually for unused Personal allowances if on PAYE: unlikely to affect you in any case as you are leaving at the tail end of the tax year, you would have been as much on taget as is possible with PAYE.)
However, I would send in a P85 anyway. Nobody will look at it, but the copy you keep will be a useful reminder (dates etc) for you when you do get around to doing your Self Assessment. And also, if anything does go pear-shaped,you can tell them you told them. :) It's a shame they withdrew the old P86 (I'm coming to, or back to, the UK) form. It was useful for bookending departures and arrivals clearly, because if questions do ever arise, they always arise ages after you've forgotten all about it.
Any ideas about how to get a reply to letters to HMRC? Or what the average response time might be?
Probably just in amateur league here, I mean November 2022 probably looks like indecent haste on my part.
Every scrap of information has been provided, but as a top-slicing relief calculation with 2 different sets of relevant years is needed, I guess it's gone into the "too difficult" tray. (To be fair it is a bear of a calculation.)
Copies and reminders sent, naturally,
I would get my MP involved, but nobody would have any respect for him anyway.
Can't even complain to a proper DI anymore. But I'm coming up to my OAP, I'll soon be able to go and shout at strangers in the street soon, which is something...