Just looking through all the new pictures that have been uploaded to A.net (some excellent ones too) and i came across an AA B777:
Photo © Christopher Hammarborg
Now this was taken at LHR and I spotted this plane at LGW on the same day!
Could this be an arrival from the US to LHR to drop off then transfer to LGW to pick up for another trek to the US?
Probably answered my own question, but it threw me for a second !