There are a number of A320/1 flight crew who are LHR based but live in manchester, they would of course luv there to be a MAN base, but sadly there isn't one, so they commute to LHR, then start their day from the sunny south.
On the other hand there are A330 Longhaul crews who are MAN based (only a few), who are Multi Fleet Flyers who also operate the A320/1. Perhaps it is one of these chaps (chapesses) you have seen.
Life in aviation is always a lot more complicated than you think !!
Moley.