Alas, due to the principle of Direct Effect (established in the European Court of Justice case Ratti in 1978), the government have no choice in whether or not they implement directives - they have to, under EU law. How they implement it is up to the government in question, but they have to implement it and achieve the desired intent of the directive (i.e. no sneaky stuff to get out of it). If they don't (within two years of the directive being made) they can either be sued in their national courts by individuals affected by the directive (in this case, disabled people could sue our government if an EU directive were made requiring disabled people to be allowed into the Armed Forces), or another member state or the EU itself may institute the Article 234 procedure, which can lead to mega-fines.