Pension would be upgraded, but you would need to be there for 6 months before availing yourself of NHs and other benefits. You would also need somewhere to live as housing wait lists are very,very long . You would have to be very desperate to return as the uk seems to be in the process of collapse. On return to Thailand pension would again be frozen unless you play/fiddle the system and maintain a uk address.UK are looking into some folks bank accounts and it is rumoured that Thai authorities to assist uk in tracking down delinquents.
There is a world wide Campaign on frozen pensions but after 50 or so years it has been unsuccessful despite the totally unjust system.
‘Despite having paid in to the system for over 35 years mine has been frozen for over 10 years and battling inflation here.
‘The obvious messages to take in is never rely on the state to look after you in old age and be careful where you live in retirement. Philippines may be an option for you.