As with the above posts, I sympathise with the guys n girls who may lose out with the move North.
However, having looked at constructive dismissal (and various other ways to get some justice from my last employer) you really have to have a watertight case and have followed a strict set of procedures before any lawyer will even consider your case. Unfortunatley for you Manch guys, the fact that you are on a mobile contract and, as stated earlier, your employer is obligated to offer relocation when closing/moving premises, which they have, means you dont have a case at all.