I have used Isle Valley for vetting. The vetting itself went smoothly but the report didn’t arrive which caused issues with the insurance and in the end they sent a scanned version which was barely legible.
I used these a couple of years ago and was very impressed. I attended the vetting and he explained every step of the way. He also rang me later in to make sure I didn’t buy the horse !
You could try Andrew Walker (Walker Equine) or western counties. B&W might cover the area so are worth a call, I know Duncan visits a yard just up the road from Martock. Or you could try Luke from Summerleaze, they’re based in Axminster but would be worth a call. Also the Stables Equine, they are in Wells but might cover it, I don’t know them though. We’re in a funny spot in this area as we’re on the edge of a lot of practice areas and not really in the middle of any!
I was going to suggest Stables Equine, I’ve not used them myself but have heard good things.
My vet travelled from Frome to Bridgwater to do my vetting, but not sure if that’s because I’m an existing customer. You could always ask: Belle Vue vets, Trudoxhill.