A lot will depend on the RAF mission description. If it is admin support, the 525 will compete well. If it involves combat requirements, the ballistic survivability and crashworthy requirements imposed by the US Army in all aspects of the design, ( just one example: to include for instance rotor blade survivability to 23MM HEI hits at various angles ( and provable by actual firing tests ) but the list is pretty long ) will be in play.
But basically those same requirements applied to the AAH competition, so the Apache specs in that regard should be familiar to the MOD folks.