It looks like I'll have to make a journey very shortly back to the UK and stay a while  (have multiple re-entry visa) and may have to re-new my passport when there. I will need a "retirement" extension of stay in mid November. (need new passport for that)

My question is : Am I likely to have any problems re-entering with my  current 'extension' in a cancelled passport while entering Thailand with the new one?

Thanks for any information.

No problem to enter the country. 

You will use both passports on entry to use the re-entry permit in the old one. Immigration will stamp you into the country in the new one.

Then you will need to go your local immigration office to have your stamps transferred.

18 hours ago, ubonjoe said:

No problem to enter the country. 

You will use both passports on entry to use the re-entry permit in the old one. Immigration will stamp you into the country in the new one.

Then you will need to go your local immigration office to have your stamps transferred.

Thanks ubonjoe. Big relief to know in advance.. 

21 hours ago, ubonjoe said:

Then you will need to go your local immigration office to have your stamps transferred.

@Lemonltr- please note that your office may require you to obtain a pro-forma letter from the Embassy to facilitate this process.