Given one the main problems faced by the British state at the moment is the greater cost of outsourcing for worse service, I'd hope they would buy the AW149s with a significant spares package outright, and maintain them internally, lest we end up with Thames Water in helicopter form.
Britain does not need V-280s for the extra range in the Pacific, Britain will not be fighting in the Pacific, our greatest involvement in any such war will be to replace US forces in Europe to enable them to be diverted to the Pacific. Plus it's not designed or made here.