Heathrow, Stansted, and Gatwick are required to pay fines to airlines when queue times exceed certain targets - known as the "Service Quality Rebate Scheme".
So, naturally there's an incentive for BAA to manipulate these queuing time figures. They've been caught doing it before, sounds like they're up to their old tricks!
http://www.bbc.co.uk/news/uk-england-london-15293612