skydriller - the problem is not an easy one!
The airlines have no choice but to let BAA get away with it! It's not as if British Airways can threaten to pack up and go to Shoreham-by-Sea airfield or base its operation at Prestwick - even if we did, the BAA would not take the threat seriously as indeed they wouldn't from other airlines either!
Indeed, when Ryanair threatened to drastically cut their winter timetable and shed jobs at Stansted if BAA didn't cut its charges, the BAA called Ryanair's bluff and now 60 Ground jobs and about 40 flying jobs are being axed. BAA plc really takes the biscuit for hard-nosed effrontery! (Much as I dislike Ryanair, Michael O'Leary did have a very good point and I hate to see jobs in this industry being cut unnecessarily!)
Like it or not, the BAA are our landlords and all we can do is put up with the sorry situation - indeed, to go one step further at ground level, we have to work with the men and women in green so a mutual spirit of co-operation is essential if we're going to achieve anything! Unfortunately, many of the problems with which Heathrow finds itself ensnared are HM Government's own making (through the shiny-bums' interference at the DFT!)
Whilst Terminal 5 will be occupied 100% by British Airways, (at this stage anyway - as we all know what government interference did with Gatwick's North Terminal and Heathrow's Terminal 4 don't we!), it will still be owned and managed by the BAA so watch this space!