No you don't. You will get either a 15 day or 30 day stamp. After this time is up, you have to leave the country, (even if is just to the border with a neighboring country) then you can re-enter and get another stamp.
If you plan on staying in thailand for a while and are now in the uk, I would suggest getting a visa from the thai consulate in hull.
If you plan on staying in thailand for a while and are now in the uk, I would suggest getting a visa from the thai consulate in hull.