My current passport is almost full, enough space for my next visa extension stamp & a reentry permit.

Was planning to get new passport this month but now have to do a trip back to the UK earlier than planned.

Will get new passport when I am back there.

So, on my return to Thailand will have old passport with visa & reentry permit. But Immigration will have to stamp me into Thailand on my new passport.

Is this allowed? Anyone done this before?

You can use both passports on entry. Show your re-entry permit in your old one and they will stamp you into the country in your new one.

Then go to immigration to have your stamps transferred to the new one,.

Thanks for quick reply. Put my mind at rest. ☺