I'm looking for some guidance on how to treat UK VAT to a client based in Guersey please. They will be taking a telephone answering service where they forward their phone number to one given by a client who will then answer the phone and book appointments into their diary. They've said they're exempt, but from what I've seen it looks to me like VAT should be charged. Is the supply in this case classed as in the UK or in Guernsey?
Guernsey is not in EU, so outside the scope of UK VAT.
But, you need to determine where the supply will be deemed to have taken place. Usually the supply is deemed to have taken place at the client's address, but there are exceptions.
I would call the VAT helpline, they should be able to point you to the relative guidance which will give you the answer.
If you don't have agent authorisation for VAT, just call HMRC and tell them that you have a general query. I tend to do this whenever possible as I don't like to give HMRC any information about my clients that I don't have to!