If there's a group of you and it's one or two journeys, taking a cab is often cheaper than the London Underground or a bus. There is a graph of number of passe

If there's a group of you and it's one or two journeys, taking a cab is often cheaper than the London Underground or a bus. There is a graph of number of passengers and price and distance and often if it's over 3 or 4 people, taking a taxi may well be cheaper than public transport more times than not. A black cab can usually seat about 5 people with luggage. (Of course it doesn't apply if everyone has already paid for their public transport tickets via a pass, and does depend on distance and time of day etc etc) This also applies in many other cities and towns, even more so because the taxis are cheaper and the roads less busy and the distances smaller. I particularly recommend it for families with children and luggage where the tube is a night mare, or for groups of friends going out at night. Of course private hire (e.g. uber) will be cheaper still.