Far from the longest taxi trip, but one that worked out well.
A late Saturday evening Virgin West Coast to Euston was getting more and more delayed so the guard came round asking passengers about onward connections. There was no chance of me making it to Waterloo in time for the last train to Camberley, so I was given a slip and told to turn right at the top of the ramp. I went through a doorway to find a large circus of taxis with Virgin staff trying to match passengers to destinations that cab drivers were prepared to go to.
It came to my turn and said I was going to Camberley. No other passengers were interested so I knew I'd bagged a solo ride. The drivers were asked "Anyone for Camberley?" and one piped up and said he'd do it. Once safely heading away from Euston, he confided that he'd been working all day in London and was about to head back to his home in Frimley, about a mile away from where I lived. He was very happy to be paid for going home and gladly dropped me at my front door. The bonus being, the trains to Camberley are so slow I was back home 15 minutes earlier than if the train had run to time.