Why did David Cameron announce two years ago that he believes there should be a referendum on Britain’s relationship with the EU?  Was it because this pragmatic politician thinks that he should take a leap in the dark and risk splitting his party – simply because there hasn’t been a plebiscite since 1975, and Britain’s membership now requires democratic endorsement?  Or was it because he became convinced, amidst rising pressure from his own party and the growth of UKIP as an electoral force, that the only available means of keeping the Conservatives together was to concede a popular vote?

There is no great mystery about the answer – and the question that follows is whether the Prime Minister is now going to carry on where he left off.  This is a big Parliamentary week for the EU referendum plan that he first announced in his Bloomberg speech.  On Tuesday and Thursday, the Referendum Bill will be debated in committee, and today’s papers are packed with details of the main issues at stake: purdah (or rather the lack of it), the length of the campaign, the date of the vote.

It may yet be that other EU countries concede nothing at all to Cameron, and that he flies back to Britain after his renegotiation ends to recommend a No vote.  But to write that possibility is also to show how remote it is.  The Prime Minister has always believed that Britain should remain in the EU, and by far the most likely outcome is that he will return to campaign for Yes.  In which case, he will want to win it. And in order to win it, he wants it to be held on the most favourable terms possible for him.

These appear to include a short campaign (so that No has no time to gather steam), a possible vote on the same day as the Scottish and Welsh elections (to boost Yes, or at least that’s the theory), and no purdah (so that the machinery of government can weigh in – warning that a No vote will unleash the economic equivalent of a nuclear winter, in which giant rats devour the eyeballs of newborn babes).  As presently drafted, the Bill allows for all of them.

One could get hot under the collar about all of this, and fulminate about how fixing the terms of the referendum to get a result one way or the other would deprive it of democratic legitimacy.  But there is a more simple point to hand.  There may be no Commons consensus for these measures at all – particularly the proposed suspension of purdah, which has led to protests on the floor of the House from all parts of the Parliamentary Party.  After all, the Government’s majority is only 12.

Furthermore, sympathy for a fundamental renegotiation, and indeed for Out, runs from brand new backbenchers all the way to the Cabinet.  In today’s Sunday Telegraph, it is claimed that Conservatives for Britain, the new organisation headed in the Commons by Steve Baker, now has over 100 supporters, including some Cabinet members.  The Wycombe MP won a notably warm response to his new initiative from Chris Grayling in the chamber last Thursday.

There are twists and turns ahead this week, as whips and backbenchers alike seek to group amendments in ways that will suit them, with the Speaker making the final decision on selection. Much will also depend on what Labour decides to do.  But looking ahead only returns us to where we set out.  What is the priority for Cameron?  Getting the terms for the referendum he wants, or keeping his Party together?  Will he further the drive for unity that he began at Bloomberg?

The Prime Minister has made a fresh start with his Party since May 7 – carrying out a reshuffle that was as well thought-through as last summer’s was carelessly constructed.  So have some of his backbench critics.  They may not care for him, but have recognised, as they should, that by winning a majority he has gained a new legitimacy – indeed, on one measure he is now the most successful post-war Tory election-winner since Margaret Thatcher.  There is a way to deepen this common sense of purpose.

Readers of this site will be familiar with it.  On the one hand, Eurosceptic Conservatives should stop calling for what the White Queen in Alice in Wonderland called six impossible things before breakfast. These have included, at one time or another, the “mandate referendum”, abolishing Articles Two and Three of the 1972 European Communites Act, and that fundamental renegotiation which would sign Britain up to a free trade area with Europe and very little else.

There is no mandate for any of this in the manifesto on which Cameron has just won a majority.  Indeed, it unambiguously commits Britain to the single market – and the single market means single rules with a single EU-wide court to rule on them.  The Prime Minister wants no British participation in Eurozone bail-outs, lower EU spending, protection for the City of London and curbs on EU-wide benefit entitlement.  He should be left to get on pushing for them.

But on the other hand, he also should complete the task on which he was furthering at Bloomberg: building Party unity.  That means giving Ministers who want to campaign for Out – and believe that his renegotiation aims don’t go far enough – the freedom to so so when the campaign comes.  It also entails a level referendum playing field: a longer campaign, no overlap between the referendum date and that on which other elections are held and, above all, the retention of purdah.  But perhaps this Grand Bargain is too reasonable to appeal to extremists on either side of the debate.