Woohoo!! My question got answered on the FT "Ask the experts" website. Last week, in honour of the 20th anniversary of Big Bang, the deregulation of the financial markets in London which led to its growth in importance as a financial centre, Sir Nicholas Goodison, former chairman of the LSE, wrote an article on "whether London can stay at the top" and answered questions on the FT website. His article was broad but pretty interesting, as was his answer to my question (scroll down near the bottom of the page).