Patricia Hewitt has urged sceptical business leaders to back the campaign for a Yes vote in the referendum on the EU constitution.

In a speech at the Mansion House in the City of London last night, the trade and industry secretary conceded that the European Union was "unpopular" and that ministers had failed to make the case for membership with sufficient conviction.

Hewitt said: "Business leaders are increasingly sceptical about Europe. And we in government have not yet done enough to persuade you in business, or the wider public, of the advantages to Britain of our EU membership."

Meanwhile, the Conservatives have criticised the government's decision to start campaigning for a Yes vote on May 8 - the 60th anniversary of VE Day.

"I cannot think of a more inappropriate way to celebrate the 60th anniversary of VE Day," Tory leader Michael Howard said.