Foreign exchange turnover in London each day is of the order of $2,000 billion, with the bulk of it at much finer margins than our bank has just made on its $1.6 billion trade. Banks do occasionally charge fees for arranging options and derivatives to currencies, but the greater part of the income stream from foreign exchange activity consists of profits from deals of the kind described. Many people would regard such profits as speculative winnings from short-term jockeying, and as justifying the epithet "socially useless" in much the same terms as the work done by croupiers in casinos or bookmakers at racetracks. 

But don't mock. In the year to the third quarter of 2011 the UK's exports of financial services — predominantly from the City of London, and mostly arising from trading profits, commissions, fees and such like — totalled £42.3 billion, about 3 per cent of our national output. The UK's surplus on trade in financial services was somewhat smaller, at £31.7 billion, as British companies carry out some foreign exchange trades elsewhere than London, issue securities in New York and Hong Kong as well as the City, and so on. At any rate, the massive surplus on international financial services is basic to the UK's ability to pay its way in the world. 

In the third quarter of last year the UK had a current account deficit of £15.2 billion, said to be the highest on record. Bluntly, the City is vital to its international creditworthiness. In broad terms, without the surplus on financial activities, the payments deficit would be twice as large as it is. If excessive regulation were to cause banks and other financial institutions to relocate, we would face the challenge of having to develop new export products and industries in a highly competitive world marketplace. A disturbing trend is that in the last few years the UK's imports of financial services have been growing at a much faster rate than its exports, although they remain smaller for the time being. That trend may partly reflect British officialdom's attack on the banks and the consequent emigration of highly skilled professionals. Croupiers and bookmakers may be disliked, but they tend to be well paid. Financial markets always resemble casinos to some degree. It is better to have large, successful and productive casinos in our own country than to overregulate them and push them abroad.