Test four: UK financial services industry

The World at One examines the chancellor's fourth precondition for the UK joining the euro - the impact on the City of London and the financial services industry.

According to Gordon Brown, membership of the single currency and Economic and Monetary Union "would affect the financial services industry more profoundly and more immediately than any other sectors of the economy".

Gordon Brown's five economic tests

Can there be sustainable convergence between Britain and the Eurozone?

Is there sufficient flexibility to cope with economic change?

What will the effect be on UK investment?

What will be the impact on the City and the financial services sector?

Is it good for employment?

Rather like the investment test, this test is a matter of deciding whether present success would be enhanced or endangered by joining the euro.

To take just one example, London's share of the lucrative Eurobond market - denominated in euros - has actually been rising since the single currency was introduced, from 48% to 54%.

Makes no difference?

Here's the former chancellor Ken Clarke:

"I would not have put the weight upon this that Gordon Brown did.

"I think that really it scarcely makes any difference one way or the other to the pre-eminence of the City compared with far more important things like levels of taxation, and the levels and style of regulation imposed on the city by the government," he says.

"That matters far more for the long-term future of the City of London."

But you can argue this case back to front as well - which is what David Lascelles does from his think-tank at the heart of the City.

"It's proving to be, at the moment at any rate, a magnet for Eurozone business.

"It's interesting to note that London does more international euro-denominated business than both Paris and Frankfurt put together," he says.

"I don't see any evidence that the City has suffered."

He points out that the Frankfurt Stock Exchange, when looking for a partner to merge with, decided to team up with London rather than Paris.