EI/UA contract is up in March 2013 and its unlikely to be extended.
And aren't United renting slots from Aer Lingus at Heathrow at the moment. Maybe Aer Lingus will also stop this agreement from March 2013, take the slots back and be able to launch a UK route from LHR, and then if they manage to buy new slots, they could start even more UK routes from LHR.