Like an unwanted Valentine’s Day gift, David Cameron’s package of European “reforms” has been spurned. First, the press panned it royally; now the public have sent it back to No 10. A new poll in The Independent on Sunday finds that six in ten people are braced for a “bad” deal at the EU summit this week, with only two in ten expecting the PM to come up smelling of roses.

Of course, Cameron is spending the few days left before the summit trying to cram some extra goodies in the box. There is talk of a benefits squeeze for EU migrants lasting seven years and renewed efforts to beef up UK sovereignty by giving our Supreme Court powers over the European Court of Justice and by enshrining parliamentary sovereignty in domestic law. These essentially cosmetic measures might be enough to give Boris Johnson a fig leaf for a retreat to the “Remain” camp, but it looks like the public has already made up its mind. Cameron’s much vaunted renegotiation has proved a damp squib.

Plan A was to reprise Harold Wilson’s so-called renegotiation of our terms of membership in the 1970s. First, talk up a package of piffling changes as fundamental reform of our relationship with Europe, then manufacture some rows with intransigent foreigners, then emerge bleary-eyed from the summit and declare victory – “game, set and match,” as John Major put it after sewing up the Maastricht deal – the one that fixed us firmly on the road to a federal Europe more than 20 years ago.

Well, it looks like Plan A will have to be junked. The public is not buying it, nor does it look as if the public can be persuaded to change its mind. True, the Remain camp holds a slight but steady advantage over the Leave camp in the overall opinion polls. But if the referendum is framed as a verdict on Cameron’s renegotiation, then it looks like he’s in trouble.

Of course, that is the problem with referendums. Voters cannot be trusted to answer the question on the ballot paper. General dissatisfaction with the government, a sudden shock to the political system showing either Europe or ministers in a bad light, or too great a focus on Cameron’s negotiating prowess are all capable of skewing the result in an unfavourable direction for No 10.

Then there is the way the referendum has become entangled with the marathon to become the next Tory leader, given that Cameron will step down before 2020. Ministers – and future leadership contenders – weighing up their options as the summit approaches are trying to calculate how their hopes of glory might be advanced or damaged by the attitude they strike towards the European question.

It is not an easy calculation. Generally speaking, it helps to be on the winning side. So if Remain, the favourite with the bookmakers, triumphs those who take this option might be expected to profit. Certainly, George Osborne’s chances of succeeding Cameron would be strengthened by a Remain victory. In which case, Johnson, hellbent on putting his personal ambitions before both party and country, might well find himself having to settle for the lesser prize of a senior Cabinet post in an Osborne administration.

But it is not as simple as that. A narrow victory for Remain – in the face of an overwhelming vote against the EU by highly Eurosceptic Tory activists – might play into the hands of whichever Tory comes to dominate the Leave campaign. In the final run-off for the leadership, the sceptic candidate would be perfectly placed to cash in on a good war.

A victory for Leave would almost certainly hand the premiership to the dominant figure on this side of the fence – hence the recent surge in grassroots support for Liam Fox.

To come back to Plan A. If that is junked, then Plan B comes into play, the one that Cameron gave a gentle canter to while visiting Angela Merkel in Hamburg last Friday. If the public has decided that the renegotiation package does not amount to a row of beans, the PM will have little alternative to fighting the referendum at a more fundamental level, almost as if the attempt to improve our terms of membership had never been made.

There may be desperately little evidence for this proposition but expect the Remain camp to seek to reframe the argument in terms of security. Economic security, yes, in terms of the prospects for jobs and living standards, but national security too in terms of combating threats from terrorists at home and enemies abroad.

In Hamburg, Cameron linked Britain’s EU membership to the fight against Isis. “Just as Europe has faced down dangerous and murderous ideologies in the past, so again we must stand together in this, the struggle of our generation, to confront this evil and defeat it.”

Quite how the PM thinks that a weak and incoherent EU, lacking an army and incapable of securing its borders or conducting any sort of effective foreign policy, can keep us safe in our beds is another matter. Some of us will continue to believe that our security is best protected by the alliance with America and Nato.

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