For example, for a cab Manchester to London (or London to Manchester, of course), you can find an affordable transfer fare, especially if you book ahead of time. You can also choose from different types of cars, from an executive car that carries three passengers, up to a minibus which carries up to eight passengers.
The drivers are licensed professionals, and they can pick you up at all sorts of popular points in and around London. They have fixed prices for common journeys, so you know what to expect, and nobody will be playing any games with the meter! Submit the info about your journey using the "request quote" feature on the London Drivers site, and plan your travel budget accordingly.