Can I enter Thailand by land if I have 2 arrival stamps by air within the past year with a UK passport?

Yes, as a UK passport holder, you can enter Thailand by land even if you have two arrival stamps by air within the past year. The rule states that nationals eligible for a 30-day visa exemption can enter through land checkpoints twice a calendar year, and previous air entries do not count against this limit. However, additional entries may be at the discretion of the immigration officer.