With over 4,000 Blackhawks being operated by 28 Nations.....that seems a pretty good endorsement along with many NATO nations being in that number....commonality of parts and the ability to piggyback a new customer onto the existing logistics system should also be a plus.
Building the aircraft in the numbers the MOD is seeking seems a bit expensive if a totally new design is selected....and the value of all of the spares over a long period of time would offset the short term benefit of buying British for the airframes.