When Liam Fox, one of the Cabinet’s leading Brexiteers, assesses the chances of Brexit happening this year at roughly 50/50, this should serve as a clarion call to those of us who hope a second referendum will give us the chance to reverse Brexit. There is a huge amount of work to do if we are really to achieve this.

Remain campaigners have to get three things right, and fast: they need a fresh attitude; they must agree early on their messaging; and they need a clear idea on the question they think the referendum should answer.

The attitude is maybe most critical, and most difficult. It can be summed up in the word humility, which does not come naturally to all remainers. A second referendum must not be about showing that we were right all along, and leavers were wrong - however intensely we might believe that. We must show a serious willingness to learn the lessons of the last referendum, and invite our counterparts to do the same.

Many remainers discovered with dismay, even disbelief, that most of our fellow citizens did not share our perception that our country’s prosperity, maybe even our identity, had become positively and irrevocably entwined with our EU membership.

We need to accept that many people did not feel part of that prosperity, they did not identify with Europe, and they often felt a pronounced aversion toward the metropolitan classes they saw as most benefitting from our EU membership. Even more important, we had no answer to people’s discomfort, occasionally but generally not racist, with the number of foreigners coming into our country. Even if only half of these migrants were European, this will need to be addressed if the referendum is to be won.

For their part, we must hope that leavers will recognise that Brexit is far more difficult to carry off than their campaigners suggested last time around. That is precisely why it has been so difficult to make it happen. Boris Johnson memorably crystallised the illusion in his ludicrous assertion that we could ‘have our cake and eat it’. What Mrs May’s Brexit strategy has shown, in her honourable and dogged - if doomed - attempt to square the circle, is that we cannot both stay part of the EU’s co-prosperity sphere, and strike out pluckily on our own.

The collapse of the Brexiteer argument for the UK as an autonomous trading power between the great blocs of the US, China and the EU, has been striking. Between Japanese disquiet, Chinese contempt and typically brutal and ambiguous soundbites from President Trump, most recently reiterated by the US Ambassador in London, it is clear that there is not a great wide world out there desperate to offer special trading terms to the UK. The words ‘regulatory superpower’ are not very attractive, but we are discovering, in all sorts of areas, from industrial supply chains to food and environmental standards to technology, that we can either be part of the EU sphere of influence, ideally as a rule-maker, or we shall be disgruntled rule-takers of no fixed abode and with minimal influence.

What are therefore the messages we need to project when the opportunity arises? Some of them have not changed, since the slowdown in economic growth and the shortages of nurses for the NHS (in absence of EU nationals), have happened as forecast. Those arguments must still be made:

* That we are far stronger and more prosperous within this imperfect and still developing Europe than as a querulous dependent outside. European values and standards are actually ours – we helped to shape them - even where we very occasionally disagree on particular policies. Our current levels of prosperity do depend on these values and standards.

* That we will be protected by the privileged status that member states still appear willing to give us, so that we do not need to join their troubled monetary union. Nor do we need to be part of the Schengen area, which really does remove border controls – and which our traditional status did not. We failed to make that clear in the last referendum.

* That a convinced British voice, alongside like-minded countries from North – the eight-nation New Hanseatic League - and potentially from East and South if we play our cards right, will always head off unacceptable infringements on sovereignty. Who can name any domestic political initiative in recent years that a British government was prevented from implementing?

In the ‘lessons learnt’ category, the following new points should also figure:

* Those parts of our country and our cities that have suffered from the uneven rewards of European integration and globalisation do need special attention, in the spirit of Mrs May’s Downing Street remarks when she became Prime Minister. And those areas most adversely affected by immigration – especially with respect to health, housing and welfare services – should qualify for targeted assistance. It is only on the back of the higher growth and economic prosperity that EU membership makes possible, rather than the declining growth rates that every Brexit scenario anticipates, that we shall be able to afford such a programme.

* Europe’s external borders will need to be policed far more effectively in our shared common interest. David Cameron’s request for an ‘emergency brake’ was wrongly rejected by the EU. But the likelihood in the next few years, if we look at what is happening in European politics, is that all EU countries will be demanding one. We need to be part of this debate, not pretend that we can opt out of it as the tides of migration will affect us either way.

So what is the right referendum question? It has to be binary. Shrewd and principled mavericks like Justine Greening must recognise that referendums are not multiple-choice questionnaires. As soon as three options are given, there is a huge risk either of misunderstanding, or of confusion in how ‘second preference’ votes are allocated – when they are actually cast. Debates about alternative votes, STV choices and two-stage processes are fine for academics and Whitehall to debate, but not for practical politics. The simplicity of the question is the saving grace, as well as the polarising danger, of a referendum. There could be three binary questions:

* The choice could be Mrs May’s draft agreement versus Leave (undefined) ie hard Brexit. This would honour the first referendum, offering Leavers a harder form of Brexit and remainers a ‘soft’ if deeply flawed option. Fortunately for remainers, Parliament, which would be responsible for the question, is unlikely to allow a choice that excludes the status quo, which is Remain.

* Option two would be Mrs May’s Plan against Remain. This would have the merit that both options would be real: one is a detailed and worked-through draft European Treaty, albeit one that looks unlikely right now to find favour in the House of Commons. Mrs May would be taking it over the heads of the politicians to the nation, as in the case of the first option above. And with Remain, voters would know what was on offer. The hard Brexiteers would argue, with force, that their own preference had not been tried and was not on the table.

* Remain against (undefined) Leave. The disadvantage is that this would appear to be a re-run, inflaming those who believed the ‘elite’ is determined to reverse a popular judgement. The rationale would be that in the last referendum, the Leave position was simply too ambiguous, admitting too many varieties of Brexit: this time there would be an implicit political acceptance in light of experience that Leave would mean a clean break ie a hard Brexit. As Tony Blair has said, every remainer would have to accept the outcome, however small the majority, however harsh they thought the outcome. And a vote for Remain would clearly represent the opposite result.

This observer would go for the third option, but there is currently no consensus within remainer ranks. The discussion still has some way to go, and Brexiteers must not be permitted to divide and rule because we cannot make up our mind on what question the People’s Vote is meant to answer.

Would another referendum entrench division for another generation or so? Certainly the scars would remain - we live with them now, and they would test our society for some time to come. But British society is resilient, and division is in the nature of politics. For a decision that has turned out to be as difficult, delicate and even existential for our political system as Brexit has turned out to be, this final test of opinion should be both cathartic and decisive. It would demonstrate that a mature democracy can think twice. It could confirm the UK’s determination to leave the EU at all costs. It might also show that a democracy can change its mind.

Michael Maclay is Chairman of Montrose Associates. He has been a diplomat and journalist and was also Special Adviser to former CGE President Rt Hon Lord Hurd of Westwell.