Is there a limit on how many times a UK citizen can visit Thailand for 30 days without a visa in a year?

There is no official limit on how many times UK citizens can enter Thailand under the visa exemption rule for 30 days. Travelers have shared experiences of multiple visits within a year without issues, although it's suggested to avoid back-to-back visits and to have proof of funds or a return ticket if asked. It's noted that while some sources cite a limitation of 90 days in a 6-month period under the visa exemption, this is not strictly enforced. Hence, as long as you manage your entries thoughtfully, frequent visits should be doable.