@Stuart ********
if you don't know the rules to bring your dog back to UK its important you check this out. Import to uk requires rabies titer testing. Its too long a process for me to write up here. You'd be best to contact one of the pet import companies like James Cargo who have pet reception centre at Heathrow. They'll send you the details if bringing a dog back in from Thailand. Or contact a Thai based pet shipping company who handle the travel documents for bringing pets into UK.
Getting to Thailand might be easy, coming back less so. Not impossible but takes over 3 months to do the process.