It can safely be said that they were going into Heathrow. The approaches for the other London airport don’t go anywhere near the centre of London. (except City but they don’t get too many 747’s or 340’s).

I don’t think it’s too likely that you saw G-LSAD. Perhaps a Turkish 321?

1L.

Yeh i was thinking that as G-LASD is based up and at MAN it could well have been a 321 i honestly couldn’t tell but to me i could see the red on the side of the fuselage and the red tail.