Leave EU

Voters would feel they had regained control over their own destiny if Britain became fully independent from Brussels, the Mayor of London said.

Boris Johnson

Mr Johnson warned that the country must be ready to "walk away" from Europe if David Cameron failed to negotiate better terms of membership. 

Mr Johnson's comments will fuel the increasingly fevered debate inside the Conservative Party about European policy, which has flared after the success of Ukip in last week's local elections. 

The Mayor's intervention, at a conference of international business leaders in London, followed an attack from the Prime Minister on Right-wing "pessimists" who believed Britain's relations with Europe could never change. 

Mr Cameron is under pressure from his backbench MPs to call a vote in the Commons before the 2015 election on a Bill allowing a referendum on EU membership. 

The Prime Minister has promised to hold talks to renegotiate the terms of the UK's membership and then put a new deal to the British people in a referendum after the next election. 

While Mr Cameron has said he wants Britain to remain inside the EU, Mr Johnson said quitting would not be "fatal" for Britain. 

Speaking to reporters at the Global Investment Conference, Mr Johnson said he remained "narrowly in favour" of staying inside the grouping of 27 member states and supported David Cameron's policy of negotiating a new relationship for Britain in the EU. 

But he added: "If that fails then yes, obviously, we should be ready to walk away," he said. "We should be ready to leave." 

The public would welcome a British exit because people would feel they had won back control over their own lives from Brussels, the Mayor claimed. 

"If we are honest, I think, democratically, it would be a shot in the arm because people would suddenly feel, yes, we are running our own destiny again, our politics is entirely independent, British electors can choose the people who are taking decisions that affect their lives. 

"That would be a very important benefit." 

However, it would be essential to ensure British businesses did not suffer from losing trade in Europe. 

Earlier, Mr Cameron had told the 300 conference delegates that he could negotiate a new relationship for Britain with Europe. 

Mr Cameron attacked the "pessimists" who believed he would fail, in a direct rebuke to Tory grandees, such as Michael Portillo and Lord Lawson, who have called for the UK to withdraw from the EU. 

"There are some pro European pessimists who say, you have to, in Europe, simply sign up to every single thing that anyone in the EU suggests. 

You sign every treaty, you sign everything - there is no alternative. 

"I think they are completely wrong," Mr Cameron said.