Advice on bringing my cat to Thailand from England!

Bringing my cat to Thailand and working through all the hoops we have to jump through.  Can anyone who has done this advise on a couple of questions please.  Do I have to apply for the EHC myself and have it sent to my vet or does the vet deal directly with DEFRA for it?  (Vet seems unsure).  Secondly do we need an EX-A form as the cat will be travelling with us on the same flight.  I know this makes me sound naive but getting reliable information is proving to be difficult.

We recently brought our cats from Sydney to Thailand. we used an exporter from Australia and also an importer from Thailand. They organised everything. Including the paperwork as well as clearing the cats from Customs and delivering them to us. They are called Pet Relocate Thailand.