Tony Blair has launched Labour's campaign for the European elections with a warning against "retreating to the margins" of the EU.

Kicking off the campaign the prime minister highlighted the differences between Labour and the Conservatives on the issue of Europe.

He said the Tories would put Britain's relationship with the EU in jeopardy because of the fierce Euroscepticism of Tory leader, Michael Howard.

He claimed the Conservatives "were opposed to any deal" on the constitutional treaty and wanted to renegotiate British membership of the EU.

"The choice is not between whether we are pro-Britain or pro-Europe," he said.

"It is whether we believe the British national interest is best served by being at the centre of European decision-making or not."

Mounting a scathing attack on the opposition, Blair said the Tories are "more extreme than ever" on the European issue.

"The Tory agenda of disengagement can only lead to either withdrawal from the EU or
climb-down and national humiliation," he said.

"This policy would only offer the betrayal of our national interest by putting British trade, British jobs and British prosperity at risk."

Tax and budgets

But Labour will also signal this week that it will not sign up to a European constitution come what may.

Gordon Brown will warn that Britain will veto the new the document unless it includes amendments to preserve the UK's "red lines".

The chancellor will tell European finance ministers in Brussels that at least 25 amendments must be made to the draft treaty in the key areas of tax and budgets.

The warning comes as the prime minister repeated his claim that he can win the forthcoming referendum on the European constitution.

Speaking during a question and answer session alongside Jacques Chirac in France on Sunday, Blair said he wanted to tackle the "politics of fear".

"You need to explain this is not something people should fear but which is progress," he told British and French students.

"The argument we have to make to people within Britain is that if we want to continue with the peace and prosperity we have enjoyed, our place is in Europe."

But he conceded that the government was facing a powerful coalition ahead of the poll.

"We should never underestimate the strength of this politics based on fear," said Blair.

"This politics of fear is always very powerful. It is the one part of politics that I know and any democratic politician knows has the ability to spark something very dangerous."

Chirac said he could not "conceive of Europe without Britain".