David Cameron has rejected claims that he would back leaving the European Union if he was not Prime Minister – amid warnings he will lose next month's referendum unless young people vote.

The Conservative leader's former aide Steve Hilton suggested earlier this week that Mr Cameron was a "closet Brexiteer".

Even those on his own side have accused Mr Cameron of a pro-EU campaign that has lacked passion.

Critics will seize on comments ha made at the G7 in Japan that the UK could find its "way" whatever the result of the June 23 vote.

But Mr Cameron insisted he was not hiding his true instincts,.

Denying the charge, he said: "I withdraw absolutely nothing I've previously said. Britain is an amazing country. We can find our way whatever the British people choose.

"But the question for us is not are we a great country, have we got a brilliant economy, have we got talented businesses, have we got great entrepreneurs, have we got amazing universities, brilliant scientists? Can we go on as we have in the past, breaking new boundaries in all these areas? The question is how do we do best?

Today former Labour Leader Ed Miliband will warn that the UK could accidentally crash out of the EU unless under-35s vote in large numbers.

Studies show that older people are much likely to want to leave the EU - and to vote - than young people.

Mr Miliband will say that young people relish the freedom of studying, working and living in Europe and know that the UK cannot tackle climate change, tax avoidance and terrorism alone.

He will add: “Young people can decide this referendum. If they don’t use their vote, the danger is this referendum will be lost.”

He will also accuse the Leave campaign of ulterior motives.

“Let’s be clear about the real agenda of those who would have us Leave," he will say.

"They are the people who are suspicious of every other EU country’s motives, who see difference as a threat and diversity as a danger; the people who want us to turn our backs on the world, who deny the science of climate change, the people who dismiss the social progress brought by the EU as burdens on business.

"I urge young people not to put their future in the hands of people who pose as progressive but would seek to turn the clock back, who claim to support working people but would get rid of their rights at work, who pretend to be optimists but who peddle division.”

"Be in no doubt: if young people don’t exercise their vote, this referendum will be lost and so will many of their futures."

He will also call on older voters to “hear the wisdom of the young”.

Pro-Brexit former work and pensions secretary Iain Duncan Smith has accused ministers of an attempt to try to get the British people "to fear the future and to worry so much that they would not vote to leave".

The former Tory leader told BBC Radio 4's Today programme: "I'm passionate about the fact that there is nothing that can stand in their way and if we are free of the European Union I am convinced that this great country will thrive and prosper - those are the words of the Prime Minister of course himself, before he decided to campaign to stay in."

Voters in Scotland, Wales and Northern Ireland are likely to choose to stay in the EU, according to the latest opinion polls.

Meanwhile, Ukip leader Nigel Farage claimed the UK had "given away our passport" to 508 million EU citizens.