How long does it typically take to obtain a tourist visa to Thailand from the UK?

You can only extend visa-free entry twice per calendar year.

The first visa-exempt entry can be extended by 30 days, but the second can only be extended by 7 days.

60 + 30 + 60 + 7 = 157 days maximum per year... regardless of whether you arrive by air or land.

Only these two extensions are possible per calendar year (!).

Visa-exempt entries themselves are not unlimited, even though some believe that unlimited visa-free entries are possible by air. This is simply incorrect.

Under certain circumstances, but only at the individual discretion of the border official, multiple visa-free entries are possible, for example, five or more.

In this case, however, your entry history in your passport and on the immigration central computer must prove that your stays were short-term (!!) like two or three weeks, and the total annual stay must not exceed 157 days (some say it is 179 days)

There must be several weeks between each entry. The aim of the new regulations was to prohibit "visa runs," where you only stay briefly in a neighboring country and then immediately re-entered.

You must be able to prove the planned short stay at the immigration counter—for example, with proof of onward travel, departure, or return journey, such as a flight ticket.

I suspect (but cannot guarantee!) that a border official would consider you a "genuine" tourist based on such short trips within a year. In that case, they should be able to see on their central computer that you never extended these short trips.

The 7-day extension is a REAL extension. It's not the same as the stamp "you have 7 days to leave the Kingdom."

At least, that's how I've interpreted the changed rules regarding visa runs after following official announcements and personal accounts for days. However, I'm still NOT guaranteeing its accuracy.

What has become clear is that "per year" is defined as "per calendar year."

Those who want to be on the safe side should obtain a single-entry tourist visa in advance for stays of up to 60+30 days.

Someone entering on two single-entry tourist visas plus two extensions, with a corresponding 2- to 4-month interval between them, would reach a maximum of 180 days "per a 1-year period" (not per calendar year – this is calculated differently!).