Media playback is unsupported on your device Media caption Conservative Fresh Start's Andrea Leadsom on calls for a new EU deal for the UK

A group of Conservative backbench MPs has published a report calling for a substantial return of powers to the UK from the European Union.

Fresh Start, which says it is backed by more than 100 Tory MPs, wants the UK to remain in the union, but with "significant revisions" to treaties.

Foreign Secretary William Hague welcomed the report.

Its publication comes ahead of Prime Minister David Cameron's long-awaited speech on the UK and Europe on Friday.

In his address in the Netherlands, Mr Cameron is expected to support a loosening of the UK's relationship with the EU, to be endorsed by a referendum.

'Gamble'

However, Ken Clarke, a veteran pro-European, who attends the cabinet as a minister without portfolio, told the Financial Times any vote would be a "gamble" that could lead to the UK leaving the union.

The longer this all goes on, the more likely the UK is to leave the European Union, Nigel Farage, UKIP leader PM and Miliband clash on Europe

"I think if Britain ever does leave the European Union, it will be difficult to adjust to our loss of a leading role in the political evolution of Europe and our reduced role in the global political world," he said.

His comments echo concerns raised in recent days by Lib Dem leader Nick Clegg, Conservative peer Lord Heseltine and a number of senior business leaders about the potential loss of influence and economic damage of withdrawal.

BBC political correspondent Chris Mason says the breadth of contributions to the debate on the UK's relationship with the EU is a striking indication of the anticipation surrounding Mr Cameron's speech.

He said Fresh Start - founded by George Eustice, Andrea Leadsom and Chris Heaton-Harris - aimed to provide a range of ideas for a prime minister attempting to strike a new deal at a time when he says the European Union is changing.

Launching its "manifesto for change", the group demanded the repatriation of key powers in order to retain the UK's "national democratic accountability".

'Fine line'

It is insisting on "significant revisions" to EU treaties, arguing for the return of control over all social and employment law, including the working time directive, which it says is a real burden to the UK economy.

If Britain is active and influential in Washington, that makes us more influential in Brussels, Delhi and elsewhere Sir Nigel Sheinwald, UK's former Washington ambassador

"In our manifesto we are very carefully treading a fine line between calling for things that are just going to be a non-starter, where the rest of Europe will say 'just forget it', and choosing those topics that are really important to Britain, that would really be a game-changer for Britain's relationship with the EU," Mrs Leadsom told the BBC Radio 4's Today programme.

"Certainly, from my conversations with European politicians over the last few months, when we actually get down to the nitty gritty of what is it that Britain wants, they don't think it's all utterly impossible."

She added: "I guess if you were to say our priority is 'more trade and less of the other stuff' that's true."

In a foreword to the report, Mr Hague said "many of the proposals are already government policy, some could well become future government or Conservative Party policy and some may require further thought".

But former Conservative minister John Redwood said the proposals did not go far enough and changes were needed in fishing, agriculture and energy among other areas.

Labour said it would support the repatriation of powers over regional policy and state aid but the UK should be pressing for "broader reform" of the EU's budget and administration.

But shadow foreign secretary Douglas Alexander said he believed a commitment to stage an in-out referendum at some unspecified point in the future was "bad for the UK's influence within Europe".

'Sidelines'

The leader of the UK Independence Party, Nigel Farage welcomed the "proper debate" about the UK's future within the union.

While Mr Cameron may get some "concessions", in calling for a renegotiation of powers, he said the prime minister was trying to "deflect" attention from the real issue of the UK's membership and delay a referendum for five years.

"The longer this all goes on, the more likely the UK is to leave the European Union," he told the European Parliament.

But speaking to the Guardian, Britain's former ambassador in Washington, Sir Nigel Sheinwald, said a move away from Europe, or leaving entirely, would diminish the UK's international clout.

He said recent warnings by the US administration urging Britain against staging a distracting referendum was "a conscious decision by the Obama administration to intervene in the UK debate".

Sir Nigel, who is a member of the think tank Business for New Europe, added: "I just cannot see any logical basis for thinking a move to the sidelines, or particularly a move out of Europe, would be anything other than diminishing to the UK's capacity, standing, influence, ability to get things done and capacity to build coalitions internationally."