I know that the 30 day airport entry stamp is extendable for 30 more days but what happens with land border stamps?

Is that too extendable ( bearing in mind that some only get 15 days whilst British Passport holders and others get 30

days ) at all?

thanks

Both can be extended for 30 days at an immigration office for a fee of 1900 baht..

All passport holders from G7 countries receive 30 day "visa exempt entries" at airports and land borders.

All such entries are extendable.

Always better (and cheaper) to obtain a tourist visa prior to leaving home.