What is the current length for visa exempt entry for British passport holders and is there a better option than a tourist visa for longer stays?

Go for the SETV

Visa-exempt entry is 30 days. If British passport holders travelling from UK plan to stay more than 30 days, getting SETV is the easier way to fly to Thailand than entering on visa-exempt and apply for an tourism extension later.

Having SETV means;

- paying less than for an extension at the immigration office

- don't have to visit the local immigration office during 45 days trip to spend half or one day to apply for an extension

- less hassle with the airline at the airport upon check-in

- The Thai embassy in London is known for its short processing time for Single Entry Tourist Visas.