I have the TP to return based on my current Passport.  I intend to obtainanew Passport whilst in UK.   When I arrive back at Suvarabhumi,with TP based on old passport with corners removed and also containing my Non-O Visa, Retirement Stamp and Re-Entry Stamp and  a new passport devoid of any stamps, what problem, if any, am I likely to encounter from Thai Immigration?

None

Show both passports on entry - normally a stamp in the old passport would say "Cancelled, valid visas remain valid" - when back in Thailand get your local immigration office to move your original entry visa and valid extension of stay to your new passport, it might cost a 500 baht fee. You should receive a letter with your new passport, which the immigration office might want.

 

Remember to update everything that use your passport number for identification, such as bank accounts and some loyalty cards, and if you don't have a Thai ID-card also eventual driver's license.