David Cameron will be faced with Government resignations unless ministers are allowed to campaign to leave the European Union in the promised referendum on Britain's membership, a leading Tory Eurosceptic has warned.
The Prime Minister has made clear that he will expect all ministers to campaign for a "yes" vote if he recommends the country accepts his re-negotiation of Britain's membership terms.
However, former cabinet minister and arch Eurosceptic John Redwood said that when the referendum comes, ministers would campaign in the way that they saw fit - even if it meant losing their jobs.
"Of course they should be free to campaign as they see fit and they will be free to campaign as they see fit. The only issue is whether they are asked to leave their government positions before they do it or not," he told Sky News's Murnaghan programme.
"This is so fundamental. What is the point of being a minister if you are charged, for example, with getting immigration down but the European Union won't let you do it.
"If you are faced with that situation the only honest thing to do is to campaign for a change in the arrangement or to campaign for out."
Mr Redwood made clear that he could not envisage voting for Britain to remain in the EU.
"I don't wish to stay in the current European Union," he said. "I could not conceivably campaign to stay in the current EU or anything like it."
'Conservatives campaigning on both sides'
Veteran pro-European Ken Clarke also warned that Eurosceptic ministers like Work and Pensions Secretary Iain Duncan Smith would not support a "yes" vote and he urged Mr Cameron to allow them to campaign for the "no" side.
"There will be Conservatives campaigning on both sides," he told the BBC1 Sunday Politics programme.
"It is up to David how he wants to run his Cabinet. I would advise him to let Cabinet ministers campaign on both sides because Iain Duncan Smith and I are not going to be on the same side.
"Iain Duncan Smith and I have both actually been committed to party unity overall. We differ on Europe. The referendum is meant to be a way of letting us resolve that in a civilised way.
"I would let the Eurosceptics have a kind of free exercise in campaigning in the referendum."
Mr Clarke dismissed demands by Tory Eurosceptics like former defence secretary Liam Fox for Mr Cameron to seek the repatriation of powers from Brussels as part of his re-negotiation.
"He is not asking to repatriate any powers," he said. "Most of the people demanding the repatriation of powers can't think of any or want to repatriate powers that would lead, for example, to an inability to tackle international crime."