ok, I must be bored, so I've done some digging.
As EZYBOH says, you can't have seen G-EZJV as that was doing ZRH amongst other trips from LTN today.
However, EZJU is missing in action!
EZJU positioned out to DUB on 29th September and the crew then positioned back to LTN in G-EZJH. G-EZJH positioned out to DUB on 17th September with the crew catching an FR flight back to STN.
So it's a good bet that it's dry leased to a 737NG operator with a base in Dublin that serves LHR.
I can't see it being FR, so has anyone any ideas?