Service supplied from Thailand to UK

Hi Guys

The is a question about the supply of services from Thailand to a UK entity. (i.e. the UK entity will pay Thailand an expense & income will be earned in Thailand).  

Am I right in thinking that a UK entity ought to deduct witholding tax if  a Thai national in Thailand supplies a service to a UK entity (i.e. effectively service export from Thailand to UK business) and the Thai national would be required to declare that income for Thai taxation (with credit given for tax withheld under the Double taxation Treaty)?

Incidentally, if the service was supplied by a non Thai national under an O-A visa would the visa requirement not to work whilst in Thailand would be infringed (although theoretically work has been done from Thailand for the UK)? I presume a way round this would be to declare income in the UK & remit it after the 12 month period with no tax implication in Thailand.

Many thanks