BA did, for a while, operate 757s into JFK from BHX/GLA, as mavml rightly says.
They used a specific ETOPS-certified sub-fleet (only 3 or 4 aircraft) for these flights, which ISTR were also fitted with a multi-channel audio and mainscreen video IFE system, and a "proper" J-class cabin (for that era, anyway), as opposed to "convertible" seats used on the European fleet.
The MAN-JFK flight is still operated with a 767-300ER, and at least one of the EWR rotations from LHR is booked on the 767. The MAN aircraft was almost always G-BNWH, until it went to be "dusked" (fitted with Club World flat beds, etc) - it now seems to be any 767 from the International fleet, and these are rotated as required for maintenance.
Cheers!
Mike