Their 767-300s Trans Atlantic are all 3 class with first class,business premium and just 80 economy seats,way to many top end for BHX.Current CO/UA 757s to EWR only have 12 up front the rest economy.
The plan is that United are converting there 3 class B763's to 2 class but they due to base most of them and operate out of EWR which would leave a lot of CO 757 around which would lightly to moved to IAD and ORD to name a few. A 757 could operate ORD - BHX. The UA 763 converted will also replace CO B762.