David Cameron has restated his opposition to the UK ever adopting the euro after a Liberal Democrat Cabinet minister said it was "unwise" to rule out joining the single currency.

The prime minister said the government's position on not joining the euro was "absolutely clear" and his own view was that the UK should never sign up to the currency.

But energy secretary Ed Davey, while acknowledging that the UK should not adopt the euro in the next few years, refused to rule it out forever.

In a move which will raise tensions with eurosceptics on the Tory backbenches, Davey said the coalition government may be "more pro-European" than its Labour predecessor and said he hoped Cameron's decision to veto a treaty in Brussels last year would be seen as a "blip".

He told the New Statesman: "In due course, this government might well turn out to be seen as more constructive, more engaged, indeed, more pro-European than its Labour predecessor."

The coalition agreement rules out joining the euro and, in its current troubled state, Davey said: "I certainly don't think we should be joining in the next few years".

But he added: "You'd be an unwise person ever to rule something out totally."

"You just don’t know what’s going to happen and given the uncertainties in our economy, I think it would be reckless to rule any of your options out."

Davey is the government's newest cabinet minister, having replaced Chris Huhne at the Department for Energy and Climate Change.

The prime minister, speaking at the London Stock Exchange, said: "The government's position is absolutely clear which is that we are not joining the euro.

"My personal view is that I think Britain should never join the euro, I've made that absolutely clear.

"I think there are many challenges we face in terms of our economy, but it is hugely helpful to have a situation where we have our own monetary policy to suit our own needs where, if we get on top of our debt and our deficit and we take difficult decisions, we can maintain the very low interest rates we need to encourage economic growth and we have the flexibility to do that with our own currency, which I think is the right answer."

Shadow chancellor Ed Balls recently signaled his belief that Britain should remain outside the euro when he said there was "no possibility of the euro being joined by a British government at any time in my lifetime".