Just thought to post a followup to my swollen battery. Apple did not care one bit while closed / on lockdown here in the UK, and all authorised 3rd parties were fully booked bar one which wanted to charge a diagnostic fee and would also not accept a mail in. As they were on the other side of London I had no option but to store the problem MBP and wait for Apple to open again. I also purchased a new 16" BTO so I could get up and running again, nice machine and I wanted one but was waiting on a refresh to be honest. Anyway, Apple opened again and I took the problem MBP in, shaved monkey took one look at it, booked it in and after 5 working days all was fixed with no charge to myself.
Amazingly poor service while on lockdown but pleasantly surprised that I did not need to argue for a cost free repair, which is the norm with any repair when dealing with Apple Store Brent Cross, London.