Nick Clegg has warned that leaving the European Union would be "economic suicide" and urged supporters to declare why they want to stay a member of the political bloc.
The Liberal Democrat leader said a "coalition for the national interest" was needed to save the UK before it "stumbled out of the EU".
Clegg accused David Cameron of pledging to hold a referendum in 2017 as a "policy fix" to placate Tory eurosceptics, who themselves had been indulging in "ludicrous myth-making".
Speaking at the London headquarters of Swiss tech firm Buhler Group, Clegg said that Cameron was "playing with fire" with the result that "Britain will get burned".
Brexiters
Nigel Farage(01 of09)
Open Image ModalThe Ukip leader and MEP is the most famous 'outer'. After his party took over a 100 council seats in May's local election's Nigel Farage is hoping to win the 2014 European elections and then gain MPs in Westminster in 2015. He has confirmed he will seek a parliamentary seat himself. (credit:PA)
Lord Lawson(02 of09)
Open Image ModalMargaret Thatcher's former chancellor and a true 'Tory grandee' revealed in The Times that if and when there is a referendum "I shall be voting out". He also stuck the boot into the David Cameron by saying the prime minister's attempts to renegotiate the terms of the UK's relationship with the EU would be "inconsequential". (credit:PA)
Backbench Brexiters(03 of09)
Open Image ModalThere are quite a few Conservative MPs who would like to wave goodbye to Brussels. Ken Clarke has said the figure is as low as 30 despite the strong eurosceptic feeling on the backbenches. However the exact number is not clear. Mid-Bedforshire MP Nadine Dorries, who remains suspended from the Conservative Party, is currently talk tof the eurosceptic town amid rumours she may defect to Ukip. Other backbench Brexiters include Bill Cash, Douglas Carswell, Peter Bone and Philip Davies and former defence minister Sir Gerald Howarth. (credit:PA)
Labour's 'Let's Leave' Lot(04 of09)
Open Image ModalMost of the anti-EU focus is on the Tory benches. But there are more than a handful of Labour MPs would would like to quit Brussels as well. Eurosceptics include Frank Field, Kate Hoey, Austin Mitchell, and Gisela Stuart.Stuart has argued the status quo is "not sustainable" and Britain should leave. (credit:PA)
Media Moguls(05 of09)
Open Image ModalRupert Murdoch has warned that the EU will "sink" the UK. The News International and boss caused a stir when he met Nigel Farage for dinner in London recently and said the Ukip leader was "reflecting opinion" with his anti-EU views.In November 2010 Richard Desmond’s Daily Express became the first UK newspaper actively to call for Britain to leave the EU, launching a ‘Get Britain Out’ campaign (credit:PA)
I'm A Celeb, Get Us Out Of Here(06 of09)
Open Image ModalOf course no campaign is complete without a bit of star power. The pro-EU camp have Eddie Izzard, who do the Brexiters have?Joan Collins, a 'patron' of Ukip, wants the UK to leave. "The EU, controlled from Brussels, cares only about itself," she said in March. (credit:PA)
The Business Types(07 of09)
Open Image ModalMost business leaders do indeed seem content with what Lawson called the "warm embrace of the European single market", but there are a few dissenters. Private equity guys Jon Moulton and Edmund Truell are two and Next boss and Tory peer Simon Wolfson has said: "Britain should stay in Europe, but only on the right terms". (credit:PA)
The Commentariat(08 of09)
Open Image ModalThere are a number of loud voices whinnying on the sidelines to say "neigh" to the EU notably Melanie Phillips, Richard Littlejohn, Tom Utley, Simon Heffer.Basically the Daily Mail stable. (credit:PA)
Edging Towards Exit(09 of09)
Open Image ModalSeveral high-profile politicians appear to be on the verge of calling for the UK to exit the EU - but just are not there yet.Former defence secretary Liam Fox - pictured here with a big gun - has said "life outside the EU holds no terror" should David Cameron's hopes of negotiating a new treaty fail.Education secretary Michael Gove is said to have told friends the UK has "nothing to be scared of" by leaving Europe.And many other eurosceptic cabinet ministers, including Iain Duncan Smith and Owen Paterson are likely to share that view. (credit:PA)
The Deputy Prime Minister said: "My great fear, in all of this, is that pro-Europeans are being too slow to wake up to the danger ahead.
"The day I dread - the day I hope never comes - is a time when it is all too late: Britain has stumbled out of the EU, and we look back to these days and say we should have done more.
"It will not be enough to speak up on the eve of a referendum. We need to start challenging some of the ludicrous myth-making by the isolationists now."
Clegg's intervention comes after Tory MP Adam Afriyie launched a rebel bid on Sunday to get a referendum on EU membership enshrined in law for 2014.
The Lib Dem leader admitted that a referendum would happen "at some point or another", even if the 2017 pledge was driven by "internal party management".