Reader question: Who knows a sworn translation agency in Pattaya?

Yes, but there is something to be said about that too.

How do you find out that there is an error in the Thai translation?
You will find out later of course, but usually it is too late. Preferably before then.

Have a second office also do the translation from English to Thai?
You can have it done, but how do you know which of the two has made the correct translation.
The first or the second? Just because the second office produces a translation that differs from the first does not mean that the first is wrong and the second is right.
You will then have to have it translated at least by a third office to compare with the first two texts. If the third party comes up with another translation, then it becomes a problem, because then office number four, etc.

You can also have a second office translate the Thai translation back into English for verification.
With a correct translation, the texts must be identical to the original English text.
But suppose it differs from the original English text, is the translation from English to Thai done correctly by the first office, or is the translation of that second office, from Thai back to English, correct?
So office number three, etc…

Personally I would do the following.
An Embassy or Consulate usually has a list of official translators they have approved.
Take a look at those lists.
It is an English text. Perhaps you should obtain information from the UK Embassy/Consulate.