Like the countries already in the monetary union, Britain will have formally to pass the convergence tests set by the Maastricht treaty of 1992.

ECONOMIST: Britain and the euro

So if the tests boil down to convergence, where stands Britain?

ECONOMIST: The single currency

The nationalist Convergence and Union coalition wants a burqa ban and to make future immigrants take Catalan-language tests.

ECONOMIST: Spain and immigration

He remains the keeper of the five tests and he alone will judge how much progress is made towards reducing those impediments to structural convergence he has identified.

ECONOMIST: Tony Blair and Gordon Brown are friends again. Really