Upvote:2
No.
I am British and visited both places this year and got entry on arrival.
Thailand is actually Visa free for Brits.
Upvote:2
Per TIMATIC, the database used by airlines:
Thailand
Visa required, except for Passengers with a British passport with nationality British Citizen for a maximum stay of 30 days.
Malaysia
Visa required, except for Passengers with a British passport for a maximum stay of 90 days
So no, you don't need visas.