Another option is to reserve a seat ex LHR with either BMI or BA - don't be fooled by the 'low cost' claims by EZY - it ain't necessarily so. The £20 transfer fee could well be greater than the saving in airfare.
If it was my money, I'd go BMI (and I work for BA!), many of our own staff pax do this
If it is post the move to T5 in 2008, then it may well be different, but until then ....