David Cameron’s referendum pitch relies heavily on the mantra a “reformed Europe”, but it would be wrong for pro-Europeans to indulge the idea that the deal he negotiated in Brussels last month is anything more than a fig leaf. The parts of it that might turn out to be modestly beneficial were either going to happen anyway or could have been negotiated without the threat of a referendum. The rest is just spin. Take Britain’s opt-out from the commitment to “ever closer union”. The phrase itself means nothing because no new steps towards closer union can be taken without the agreement of the UK’s elected government and Parliament. And because the phrase is meaningless, our opt-out from it is also meaningless.

The same applies to new rules that are supposed to act as a break on integration and the deal on migrant benefits. The threshold needed for national parliaments to reject EU proposals is actually higher than the one that already applies in the Council of Ministers and the procedure for protecting the UK’s interests as a non-Eurozone country amounts to little more than a right to be heard. It is unlikely that a major decision of substance will ever be altered as a result of either provision. Changes to the welfare entitlements of EU migrants may save small amounts of money, but they will do nothing to reduce the numbers of people coming here from the rest of Europe, as even Ministers seem to accept.

All of this leaves Cameron in an awkward spot. At various times in the last few years he has promised an ambitious repatriation of powers covering whole areas of policy like crime, justice, social affairs and employments rights. He claimed that a fundamental revision in the terms of our EU membership was not only negotiable, but an essential precondition for staying in. His difficulty in trying to paper over the chasm between what he promised and what he has delivered is the inevitable result of his own weakness and dishonesty. He won the leadership of his party by pretending to share the anti-European reflexes of its most right-wing members and has been pandering to their illusions ever since. Stripped of the pretence that the UK can pick and choose from the Brussels rulebook, he now has to concede what he has known all along – that EU membership is overwhelmingly in the UK’s interests, even without the opt-outs he once insisted were vital.

Of course, this is not what leaders of the official pro-EU campaign want people to hear. Peter Mandelson last week urged its supporters not to ridicule an agreement that gives wavering sceptics “a bridge to walk back across towards the EU”. Given what’s at stake, it is understandable that pro-Europeans should want to bury their doubts in order to help Cameron sell his case. But the aftermath of the Scottish independence referendum shows that the "win ugly" approach ultimately solves nothing. What today looks like a cunning plan to get the Remain campaign across the finishing line on 23 June will sooner or later give angry Leave supporters the excuse they need to reopen the issue once again. With every up-tick in migration flows from the EU, every Commission proposal for further integration and every controversial ruling of the European Court of Justice will come the argument that Britain was conned, quickly followed by demands for another referendum.

If the vote in June is to serve any useful purpose it must resolve the issue for at least a generation. That means giving the British people an honest account of the choice before them and trusting them to come to the right conclusion. First and foremost, it means explaining that there is an unbreakable link between access to the single market and our willingness to stick to the rules. If we value the jobs, growth and investment that come from trading in an open Europe, we also have to accept the binding regulations and policies that go with it. The choice is between shaping those decisions from within the EU or allowing Brussels to impose them on us as an outsider. Either that or we cut ourselves off from the European single market altogether and lose the biggest proportion of our trade. The greatest canard in this debate – one that Cameron has foolishly encouraged until now – is that we can embrace ‘economic’ Europe while turning our backs on ‘political’ Europe.

It’s a similar story when it comes to the UK’s international standing. There is no precedent for a country retaining a global role while opting to be a second rank power in its own continent. If we isolate ourselves from the rest of Europe, we will rapidly lose influence everywhere else. Germany will become firmly established as the pre-eminent European power by default and countries like America, China and Russia will downgrade us in their calculations. Indeed, the path to a referendum has already cost us dear. Over the last two years Ukraine has been sacrificed to the feeble diplomacy of France and Germany, while democratic standards have been seriously eroded in Hungary and now Poland. None of this has attracted a word of criticism from Cameron for the simple reason that he has needed the support of these governments to fabricate the illusion of reform. It’s hard to think of another Prime Minister who has squandered our diplomatic capital so cheaply and irresponsibly.

It will take years to undo the damage already caused by Cameron’s weak and misdirected leadership. A decision to leave the EU on 23rd June would make that damage irreversible. Only a clear and honest vote to stay in can open the way to a recovery of lost British influence. To do achieve that, pro-Europeans must now forget about Cameron’s renegotiation stunt and base their campaign on the strong arguments for EU membership that have always applied.