Britain must be prepared to walk away from the EU if sufficient reform is not achieved, Boris Johnson has warned.
In his first speech since being returning to Parliament, the Mayor of London said he believed David Cameron would be successful in his efforts and congratulated him on his "schmoozathon" around Europe.
But Mr Johnson said Britain should be ready to "strike out" if terms were not agreed, suggesting an alternative future could be "just as glorious and just as prosperous".
"We now have a government, a Tory majority, with a clear mandate to seek change and therefore a Government in the most powerful position in our lifetimes to deliver reform and improvement in Europe," he said.
"If we don't get the deal that is either in the interests of this country or of Europe, then we should be prepared to strike out and forge an alternative future that could be just as glorious and just as prosperous with a free trading arrangement."
Mayor of London Boris Johnson, arriving for his count in Uxbridge and South Ruislip, said that if the exit poll was right, "then obviously, it's a very, very clear victory for the Conservatives and a very bad night for Labour"
Mayor of London Boris Johnson has offered the Duke and Duchess of Cambridge "huge congratulations" on the birth of their daughter.
Huge congratulations to the Duke & Duchess of Cambridge on the birth of their baby girl. I know Londoners will join me in wishing them well.
Boris Johnson has said Ed Miliband "would do more damage to this country than he did to his brother".
The Mayor of London accused Mr Miliband of "backstabbing" in an interview with the Sun On Sunday - a reference to the Labour leader's victory over his brother David in the party's leadership contest in September 2010.
In a heated exchange on the BBC's Andrew Marr Show, Ed Miliband suggested Tory election adviser Lynton Crosby "had put" Boris Johnson up to the comment, telling the Mayor of London: "Come on Boris, you're better than that - don't just do what Lynton says to you."
But Johnson hit back, saying: "I'm not saying your brother presented himself at A&E with a dagger in his back but he [Ed Miliband] would do more damage to this country than he did to his brother".
Boris Johnson has said speculation Conservative candidates and donors want him to take over from David Cameron is "nonsense".
The Sunday Times reported today that the party's donors and prospective MPs are increasingly unhappy with Mr Cameron's election campaign and want the Mayor of London to become Tory leader.
"They don't - that is nonsense," Mr Johnson told the BBC's Andrew Marr.
The mayor insisted a Tory majority was "not so very far from our grasp" on May 7.
Johnson, who is standing in Uxbridge and South Ruislip, has long been touted as a potential successor to Mr Cameron - even by the Prime Minister himself last month.
Boris Johnson has quipped that the general election is like a jigsaw and that it "comes together in the end."
The Mayor of London was visiting a school with the Conservative leader where the pair were helping some children with a jigsaw puzzle.
ITV News Correspondent James Mates heard the jocular exchange:
PM and Boris help 3yr olds with a jigsaw. PM:"I have a cunning plan". Boris: "He has a long-term cunning plan". http://t.co/p6myNuqU1X
Cameron: "This jigsaw's a bit like the campaign". Boris "Yes, it comes together in the end".
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Boris Johnson has given his support to Prince Andrew in the wake of underage sex claims, saying he has sympathy for the Duke of York.
"He does a huge amount of good and a huge amount of hard work. So if you are asking me whether I have sympathy for him, of course I do," the Mayor of London told LBC Radio.
"Prince Andrew, let's be very clear, is a guy who does a huge amount of unsung, unheralded work for this country," Johnson said. "I think that people should respect that side of his work."
Boris Johnson vowed to "eat the 'Kippers for breakfast" as he sought to unite Tories and lambasted those who had defected to Ukip.
Mr Johnson hit back at "quitters and splitters" and told activists that victory in next year's general election was "within our grasp" as long as the party remained united.
To loud cheers the Mayor of London said:
Just before I begin can I check that we are all proud Conservatives? Proud of the oldest and most successful party in all the Western democracies? Do we intend to fight the next election under the Conservative banner and no others? Are there any quitters or splitters? Anyone feeling a bit yellow around the edges - like a kipper?
Only the Conservative could deliver reform to the UK's relationship with the EU, he said. Comparing the successful fight against Scottish independence with the imminent by-election battles to retain the seats given up by defecting MPs Douglas Carswell and Mark Reckless, he said:
That's our new fisheries policy, folks. First chuck Salmond overboard and then eat the 'Kippers for breakfast. We will fight them on the beaches of Clacton and of Rochester and Strood as well.