From what I understand the charge was introduced so the airport could control the taxis using the taxi ramp. There were instances of people being ripped off and "cherry picking" by some of the more inscrutable drivers and now they have to have a "pass" for the taxi ramp and fee of £1 every time they use it, which of course is passed on to the pax. The airport can now withdraw passes from those drivers who misbehave and deny them access to the lucrative airport business!
