DFC
I don't agree... it's nothing to do with the CAA or Class E airspace (although that might be a future solution... but don't hold your breath?)
the controller at B has no control over the flight after the airspace boundary
B may be unable to issue mandatory instructions outside CAS... but still has a responsibility for that flight under ATSORA. The key phrase in ChilliMonster's original post is "pointing straight at" the beacon... it seems B has released the aircraft, following liaison, into known confliction and therefore failed in their duty of care.