The drive to keep the UK in the European Union will be the Yes campaign after accusations of negativity dogged the pro-Union parties during last year's independence vote.

Ministers will today confirm that it will be eurosceptics arguing for a 'No' in the EU referendum.

No 10 sources indicated that the preferred question would read: 'Should the United Kingdom remain a member of the European Union?'

Downing Street insiders said that the wording would offer voters a simple choice.

Some experts also believe campaigners are more likely to win a referendum if they are part of a 'Yes' campaign.

The announcement is likely to mean that both the SNP and many pro-Union politicians in Scotland will be arguing for a Yes in the next major UK-wide vote.

Nick Clegg, the former Deputy Prime Minister, warned Mr Cameron that the experience of the independence referendum meant there was no room for complacency.

The Liberal Democrat leader said that in recent years he had witnessed two referendums "spin off in entirely unexpected directions".

Last year's anti-independence campaign was dubbed 'Project Fear' amid accusations that it struggled to articulate a positive vision for why Scotland should remain part of the UK.

The Bill, to be published today, will also confirm that the referendum will take place before the end of 2017.

It comes as Mr Cameron begins a tour of European capitals to discuss the possibility of EU reform with leaders.

The Tory leader has pledged to hold the vote only after he has secured concessions from Brussels.

Voters will then be asked if they want the UK to remain in a new-style EU.

Political opponents have accused the Prime Minister of alienating other European politicians and giving away his hand before negotiations get underway.

In recent months, however, the Tory leader has stepped up his rhetoric on the issue.

He has warned the EU that he can "rule nothing out" if other leaders stand in the way of change.

Today Mr Cameron is due to meet President Hollande of France and tomorrow he will meet Polish Prime Minister, Ewa Kopacz, in Warsaw before rounding off the trip with talks with Chancellor Merkel in Berlin.

A No10 source said: "The introduction of the EU Referendum Bill is a concrete step towards settling the debate about the UK's membership of the EU.

"It will pave the way for the British people to have their say for the first time in 40 years on our place in the EU.

"And as the Prime Minister has said before it will be an important choice about our country's destiny."

He added that Mr Cameron was still "determined" to deliver EU reform.

UKIP Leader Nigel Farage agreed that the wording was a "simple straightforward, unambiguous question. That much is clear."

However, the arch-eurosceptic added, "that Cameron is opting to give the pro-EU side the positive 'Yes' suggests strongly that his negotiations are so much fudge.

"He has already decided which way he wants the answer to be given, without a single power repatriated"

Mr Clegg said: "This must be the first time in living memory that a country's citizens are being asked to support the outcome of a renegotiation on a matter of such fundamental importance to its place in the world without the Government of the day coming to this House and setting out exactly what it wants to achieve.

"And because we do not know what the Government considers a successful negotiation, we don't even know for sure which side the Prime Minister will be when the referendum is finally held.

"That is a precarious position from which to persuade millions of people in a referendum who are indifferent or sceptical about the European Union."

In an apparent reference to the independence and the Alternative Vote (AV) referendums, both held while he was Deputy Prime Minister, Mr Clegg said: "Having witnessed two referenda spin off in entirely unpredicted directions in recent years, I would strongly counsel against any complacency.

"So my advice to the Government, if it wishes to hear it, is simply this - pursue your renegotiation with the EU, but spell out exactly what you hope to achieve so that people understand the choice that's in front of them.

"Be careful not to string it out so long that there is not enough time to make the wider case to the British public.

"And above all, remember that the referendum will be won through conviction, not ambivalence. Ambivalence will not succeed in this negotiation and it will absolutely not win a referendum."