Cabinet minister Chris Grayling has been accused by pro-Europe Tories of "peddling myths" about the EU after he warned it would be disastrous for Britain to stay in on its current terms of membership.
The Leader of the Commons gave what was seen as a clear signal he intends to campaign to leave the EU in the forthcoming referendum after he said the bloc was set on a path the UK should not follow.
Downing Street insisted David Cameron was "relaxed" about his comments which were in line with the Prime Minister's policy that ministers will be free to campaign on either side in the referendum - but only after he has completed his renegotiation.
However the pro-EU former Home Office minister Damian Green said Mr Grayling was "going along the tightrope" of overtly breaking the rules laid down by Mr Cameron and accused him of misrepresenting the UK's relationship with Brussels.
"I think he is peddling myths about Britain in Europe. The key myth in Chris's article is when he says there are calls for still more integration," he told the BBC Radio 4 Today programme.
"It is a very explicit and very important part of the Prime Minister's renegotiation that Britain won't be committed to ever closer union. That is actually a big change in the relationship with the rest of the EU."
In a carefully-worded article in The Daily Telegraph, Mr Grayling stressed that he supported the Prime Minister's renegotiation but left little doubt that he would be campaigning to leave when the referendum is called.
"I am someone who believes that simply staying in the EU with our current terms of membership unchanged would be disastrous for Britain," he said.
"That's why I have always believed that it is imperative that his renegotiation takes place and delivers as much potential change as possible. It is in the interests of all Eurosceptics and of our country."
Both Mr Grayling and Mr Green insisted that both sides in the Conservative Party would be able to reunite and work together again once the referendum was over, whatever the result.
However Liberal Democrat leader Tim Farron said the row underlined why Mr Cameron was "completely wrong" to suspend collective ministerial responsibility on such an important issue.
"Chris Grayling's comments reveal once again the split at the heart of the Conservative Party on the issue of Europe," he said.
"If Chris Grayling or anyone else wants to argue or vote against Britain staying in Europe then that must be respected, but they should have to resign from government to do so.
"It is ludicrous that David Cameron has decided the Government will not have a collective position on the most important decision facing our country."
In the Commons, Labour's shadow leader of the House Chris Bryant taunted Mr Grayling, challenging him to declare himself the "leader of the out campaign".
"You're really desperate to burst out of your pink shirt and mount the barricades with the banner of English nationalism," he said.