Are you being asked to take an elderly passenger to London, deliver a package on their behalf, or asked to take them to the bank?
You should expect the booked taxi to arrive on time, be driven by a courteous, well presented, licensed driver who is displaying their badge. You should also expect to get in a clean, undamaged, licensed vehicle displaying a current licence plate both inside and outside of the vehicle. If this is not the case you can refuse to travel.
The route to your destination should be, in the most part, the most direct route possible. If you think you have been driven an excessive route, then please see how to complain. (Of course, there may be extenuating circumstances that would need to be explained to you at the time of travel.)
On pre-arranged private hire journeys, the price charged for the journey should be the price that was agreed at time of booking. Hackney carriage journeys will be charged via a meter unless other agreements have been made in advance of travel