Guidelines seem to suggest prolonged contact is less than two metres for more than 15 minutes. Given the size of the airfield, I don't think I've ever been on an airside coach for that long at LTN or anywhere else for that matter!
Using coaching would not be first choice, but probably more risk from other parts of the journey. After all going out anywhere carries risks. I think I'd feel more comfortable in an airport than in a pub for the evening...