I would certainly ask - the worst they can do is to say no. I have asked before to shift onto earlier flights in the lounge or at the ticketing desk when I arrived at the airport ahead of schedule and sometimes I have been lucky, other times I have had a wait. Always HBO - wouldnt have been able to do it with a checked bag asking in the lounge.

As others have pointed out - dont spend time at LCY if you dont get onto BA1 - go to Westfield and catch a film or something!