From the stobart interim results presentation in fact the precise figure is £10.66 per passenger. Those tourists who don't pay for parking will probably get the train at the stobart operated station. Or hire a car. All of which are revenue generating. Stobart also run the airport retail themselves.
Revenue for the Stobart Air division was £10.4m (2012: £7.9m) and the divisional profit before tax was £0.1m (2012: loss £0.3m)