Millions live there, millions more visit each year - but how many really know London? Do you know when Big Ben first bonged - or even who Ben was? Why the River Thames is so-called? Which top Nazi was locked up in the Tower? Or what runs through the more than 50 miles of train-size tunnels which ring the city, stretch further than the Channel Tunnel and lie deeper than the Tube - and, no, the answer's not trains. The world's first celebrity chef,...