One of Chancellor Gordon Brown's five economic tests relates to the impact of the euro on Britain's financial services industry. The Square Mile has now become a key battleground in the euro debate.

Lord Brittan, the former EU Commissioner, argued here last week that the City of London's interests would be best served inside the euro. But most of his arguments were based on the false assumption that keeping our own currency is incompatible with membership of the European Union. This is simply not true. There is no reason why Britain should not continue to take advantage of the single market in financial services while opting out of economic and monetary union.