He must have been at EOG over 7 yrs ago to be aT LHLHR as the position as it stands now is you go to EFLHR - loose everything (apart from date of joining) - start again - then go from there.
This means if you end up at the bottom of the briefing sheet even if the person sitting next to you started 2 days before you transfered. They are still more senior in that fleet because you came from EFLGW and you loose all rights to bidding an position on the aircraft or fo transfer to another fleet when you transfer.
Happy days!