Apart from a translation, my degree certificate, UK ACPO background check and divorce certificate all needed an 'Apostille' attached to them. I hired a legal firm in the UK to carry out this onerous legal task for me.
Word of advice:- insist on having a member of your UK legal team hand carry any important documents to the Thai Embassy in London for any necessary admin processing and stamps - They informed me that while queing to get in the Thai embassy, there was one guy from Thailand in the que who had sufferred the Thai Embassy(UK) loose his original degree certificate and other important documents 3 times before he eventually bit the bullet and travelled all the way to the UK so as to handle the Thai Embassy visits himself...