Taxi fares are calculated on a combination of time taken for the journey and distance. It therefore pays unscrupulous drivers to take the longest and most congested route. In any case their charges are very high, so I suggest if possible you use London's excellent Underground, bus and rail system, using an 'Oyster' Card rather than paying cash fares
www.tfl.gov.uk
www.nationalrail.co.uk
By the taxi meter. The scale the meter uses is here http://www.tfl.gov.uk/modes/taxis-and-mi...
It is also possible to book a minicab, and then that will not have a meter and you agree the fare with the driver. Minicabs are not allowed to pick up you off the street - only black cabs can do that.
But really, why bother when the Underground and buses are so good and much cheaper?
I never use a taxi in London public transport is so good and a lot cheaper
Why....?
Edit: Like any other, with taxi meters.
