DAVID Cameron believes he is close to an historic deal to keep Britain in a reformed European Union but has vowed he will not quit as Prime Minister if he loses.

Mr Cameron is looking at holding the referendum on the UK's membership in mid-June because of the school summer holidays in Scotland which begin later in that month.

However, he would need to seal a deal at next month’s European Council.

If a deal is not forthcoming until March, then a poll is likely in early September with any further delay pushing it back to spring 2017.

The Prime Minister came in for criticism from a senior Tory MP for admitting yesterday that the UK Government had no contingency plans if people voted in favour of leaving the UK.

David Davis, who supports an EU exit, attacked the Prime Minister for his lack of a contingency plan. He said: “This is actually disgraceful because you’ve got two moderately likely outcomes; we don’t know which it will be.”

He added that having no fall-back strategy was "really serious because it’s a very complicated operation to carry out, if it happens.”

Mr Cameron admitted the renegotiation with 27 EU partners was hard work but that he was hopeful of a deal in February. He insisted the UK exiting the EU, so-called Brexit, was “not the right answer”.

“There is a huge prize for Britain; we can deal with the things that drive us up the wall about Europe. We can get the best of both worlds, that actually secures our economic future in this valuable market and also help to keep our people safe by staying together with our close allies and partners as we confront extremism and terrorism. It’s a massive prize for Britain if we get it right.”

He told the BBC’s Andrew Marr Show that the prize of an improved membership package was "closer."

Asked if that meant the referendum could take place in the summer, Mr Cameron replied: "That is what I would like to see; a deal in February and then a referendum that would follow."

Responding to the suggestion that failure to get a deal at the next EU summit would mean the referendum being delayed until September, the PM said: "Or later. I have to have this referendum by the end of 2017. To me the substance matters much more than the timing, so if I can't get the right deal in February, I will wait and I will keep going."

Of the four areas up for renegotiation, curbing welfare for migrant workers is proving the most difficult given many EU partners believe it goes against the EU fundamental principles of free movement of labour and non-discrimination between EU citizens.

Mr Cameron has insisted his proposal for a four-year ban on in-work benefits for migrants was still on the table but he was open to alternatives if they produced the same result.

Asked if there could be a compromise where Britons were also subject to the same benefit restriction and then compensated with a social payment, he replied: "I am in the middle of a negotiation. I have got hard work to do and when I have an announcement to make I will make it."

Asked if he would stay on as Prime Minister if he ended up on the losing side, Mr Cameron said: "The answer to that question is yes."

He stressed that the question put to voters would be whether to stay in or leave the EU and not "this politician's future or that politician's future".

Leading Tory Eurosceptic Bernard Jenkin backed his colleague’s stance, tweeting: “PM is right. He would be the best figure to implement Brexit if @vote_leave wins the referendum.”

The Tory leader is adopting the same tactic he deployed in the Scottish referendum campaign when he rejected the notion that the result would have consequences for his own political future.

However in 2014, as polling day drew near and the gap between the Yes and No votes narrowed, sources suggested he did indeed draw up a resignation statement, which he would have made from No 10 the morning after the result if he had lost.

Many Westminster-watchers believe he would have to do so if he lost the EU vote despite the Prime Minister's assertion to the contrary.

Mr Cameron admitted that the UK Government had no contingency plans for Brexit.

"I don't think that is the right answer for the reasons I have given,” he insisted but added: “Were that to be the answer, we would need to do everything necessary to make that work."

Asked if Whitehall civil servants were working on a plan should voters reject staying in the EU, he replied: "The civil service are working round the clock to support my negotiation."

The UK Government adopted the same position before the Scottish independence referendum. But it was widely believed that privately Whitehall mandarins had drawn a contingency plan for a Yes vote in the 2014 poll.

Politically, it was believed wise not to admit to such a contingency plan for fear this would lead to the pro-independence camp playing up the UK Government’s recognition that a Yes vote was possible.

Meantime, Tory sources suggested Mr Cameron would have his work cut out as it was estimated some two-thirds of Conservative MPs were minded to back leaving the EU.

Former Labour First Minister Henry McLeish said he would support Scottish independence if the UK voted to leave Europe against Scotland's wishes.

Mr McLeish said Brexit would spark a "constitutional crisis" resulting in the break-up of Britain if a Scottish majority voted to stay in the EU was at odds with the rest of the country.