Haven't tried it myself, but have a look here;
HM Revenue & Customs: VAT refunds for visitors to the UK It does seem to apply to goods that you will take out of the UK, rather than services you receive here though. That seems similar to the situation I get when I visit the US, I pay sales tax on any flying I do there, but can but can buy aircraft parts/headsets/avionics tax free, with a UK passport and a declaration that I am permanently exporting them.