On the whole very prompt on arriving, polite, cars clean.
Generally the drivers know how to avoid traffic jams and diversions (very important in London) by taking side roads.
On one occasion when the driver could not meet me because of a one way system, and I told him I was going to take a bus, he actually left his car and managed to find me on foot- quite extraordinary. (unfortunately when we returned to his car- in Drury Lane- he had received a £70 fine!). So I am
in their favour. However, it must be said that they are not always familiar with the London 'knowledge'