Although it will depend on the type of services provided, I tend to treat the place of a Supply of a service as the place it is received, rather than actually carried out.
So if you are providing a service to a customer in Singapore, provided it is received for their use in Singapore then the place of Supply should be Singapore. If the customer is intending to use the service you provide in the UK then the place of supply is the UK.
-- Edited by YLB-HO on Sunday 3rd of June 2012 11:39:35 AM