Minister for Europe Denis MacShane has denied dismissing the tests used by the government to decide if Britain should adopt the euro.
The government plans five tests on whether to adopt the euro
The Scotsman newspaper reports that Mr MacShane called the five tests "always a bit of a red herring" in a speech at Durham university.
It said he also contradicted official policy on the EU constitution.
Mr MacShane said any suggestion that he meant to question or criticise government policy was "barmy".
BBC political correspondent Sue Littlemore said Mr MacShane's comments came in a speech to students nine days ago, which was recorded.
He was delivering a passionately argued case in favour of Europe and Britain's involvement in it, she said.
His provocative, unscripted comments came as he spoke about the European currency and Chancellor Gordon Brown's five economic tests for joining the euro.
He said: "On the euro, and other things, we've waited for the economics to be right on that. Although that was always a bit of a giant red herring."
His remarks have been interpreted as bringing him into conflict with the chancellor and official government policy.
The Scotsman reported that on the EU constitution, he said: "Europe is very young. This treaty won't be the last word."
Mr MacShane says he was misunderstood
That would contradict the prime minister's claims that it would be.
He also said he would like to "get rid" of the Common Agricultural Policy, while official government policy is to "reform, not scrap" it.
But he has denied that he spoke against government policy.
He said he believed the five tests to be essential and had used the phrase "red herring" to describe the arguments of eurosceptics.
"The thought that, after three years as a minister, I would say anything on the euro other than what's the government's position is absolutely barmy," he told the paper.
He said he would never contradict "my beloved prime minister and my adored chancellor".
He added that he would not deny the report if that had been what he had meant by his remarks.
"A minister saying something he should not have said is fair game. But this time, not guilty," Mr MacShane said.
The Tories said Mr MacShane's comments showed he was taking sides in a battle between the prime minister and Mr Brown over the euro.
Graham Brady, the Conservatives' Europe spokesman, told BBC Radio 4's Today programme the minister had committed the "cardinal sin... of telling the truth".
'Out on a limb'
He added: "He has made it very clear that the so-called five economic tests on the euro are just a red herring, they are a political fig leaf really to cover the government's embarrassment over that, which clearly puts him on a collision course with Gordon Brown."
Matthew Taylor, chairman of the Liberal Democrat Parliamentary Party, said Mr MacShane's comments revealed the five tests were "back-of-the-envelope tests to suit the chancellor, to allow him to say yes or no to the euro as he wished".
Mr MacShane also drew criticism from within his own party.
Ian Davidson, MP for Glasgow Pollock and head of the Labour Against the Euro group, said the minister was "out on a limb".
He added: "The idea that these are just simply a red herring suggests that it is going to be politics that ought to decide whether or not we join.
"Now that is not the government's view."