Number of taxis in London?

My interview today went pretty well. It was probably the least cryptic of all the interviews I have ever had. The only mysterious question was "How many taxis are there in London?" I wont tell you my answer until you have all guessed though (they told me after I got it hideously wrong). I wonder what significance can be drawn from the answer to such a question.

I seem to give all my copy to trains at the moment, so I wont release my wrath today, except to say that as a result of signal faliures at Woking, the whole network was an enourmous disaster and despite leaving myself half an hour in case of delays, I was still three quarters of an hour late for my interview. Why on earth the station manager told us at 10.05 that the train due to appear at Farnborough 9.31 would arrive at 9.34 I will never know... Perhaps his watch was working backwards today.

Sign spotted by driving instructor outside Church in Aldershot:
'Donate an Organ: Give your Heart to Jesus'