Dear itsupport,
this is more a legal matter, the technical support can give only technical advices.
From a pure technical perspective, the product does not need to know where you have bought the license. That is, you can technically use X licenses for maximum X seats regardless where you buy the licenses and where you use them. We see this done by every international customer.
From a practical point of view, if you are going to have two stand-alone SEP Managers in the two sites (UK and Singapore), each of them will have its own seats counter, thus you won't be able to ensure you are not over-deploying the product.
If you still need a legal opinion (not a technical/personal opinion), you should contact our Customer Care and ask for licensing assistance.