In addition, they are often very reluctant to take short journeys from LHR in particular to one of our offices in Bedfont Lakes (2 mins from T4). If this should happen to you, just remind the cabbie that he/she is obligated to take you, and that if they return to LHR within 15 mins of leaving, they will not have to pay their toll fee again.
You will get some seriously dodgy looks, but you will get your taxi ride!!
Lewis