George Soros is not exactly an insurgent leader from central casting, but you certainly can’t fault the billionaire philanthropist for his frankness. “The EU is in an existential crisis,” Soros said in a speech in Paris this week, before adding: “Everything that could go wrong has gone wrong.”

With Italy compounding Europe’s woes in the wake of the Brexit vote and the rise of rightwing populism more generally, it takes nerve to choose this of all moments to launch a fightback for Europe. Yet this is precisely what Soros proposes. There’s an audacity about his approach that echoes the French general Ferdinand Foch’s message to his commander-in-chief: “My centre is giving way, my right is retreating, situation excellent, I am attacking.”

What made that bold message in 1914 so splendid was that Foch went on to win his battle. But can Soros also win this political battle against the odds? Can those who want to preserve not just the European Union project but more specifically Britain’s association with it, win theirs? The heart says both that they must, and also that they can. The head says it will require more than bravado and Soros’s money.

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The importance of leadership in politics is widely understood. That of timing less so. But success in politics, as the wily French diplomat Prince Talleyrand once observed about treason, depends a lot on dates. All politicians know there are times when public opinion is ready for change, and times when it digs in against it. There are tides in these affairs. Get them wrong, and your campaign is left high and dry. Catch them on the full and you can be swept towards your goal. So it is with attempts to save Britain from Brexit.

Back in the immediate aftermath of the EU referendum, it was futile and arrogant to insist that Brexit should immediately be stopped. That didn’t make the cause of stopping it less just or less necessary. But any such effort naturally offended the electorate’s sense of fairness. This wasn’t the time to challenge it. Theresa May undoubtedly got that.

That may be changing now. There are several reasons why the 2016 verdict no longer enjoys absolute sway. The embarrassing legacies of the referendum process are one. The slapdash amateurism of the negotiation process is another. The botched general election is a third. A significant degree of buyers’ remorse among Labour leave voters may be a sign of the change, as an assessment by the pollster Peter Kellner suggested last week.

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But the most important reason is simply that, over time, two things have become clearer. The first is that leaving the EU is long on risk and short on guaranteed reward. The second is that the time for facing that verdict is arriving. The question facing Britain in the summer of 2018 is not whether to reverse the 2016 vote, it is whether the terms of British withdrawal from the EU are terms that should be accepted or not. Time – and the efforts of the House of Lords – have started to allow that view a fairer hearing.

Or rather, they were beginning to do so before the Italian crisis exploded last weekend. Had it not been for this, it was becoming increasingly likely that the House of Commons would set conditions for an EU-UK relationship that would end in a rejection of the deal or on a significant last-minute scuttle by May herself towards a softer Brexit, a longer transition and a much closer alignment with Europe. It was becoming increasingly hard to imagine that the red-white-and-blue Brexit of which May spoke in 2016 has any realistic chance of coming to fruition.

The Italian crisis may derail some of these judgments. Carlo Cottarelli’s technocratic government is unlikely to survive for long. If Italy, as seems likely, holds early elections in which its continuing eurozone participation is a central and explicit issue, this will preoccupy not just Italians but the entire European political class. If Italy elects an explicitly anti-EU majority, this will become a full-scale challenge to Europe’s existing institutions and policies.

In those circumstances, Brexit does not merely become a second-order issue for the EU. Any Brexit deal would also resonate differently in Britain. The EU with which British MPs and voters may be asked to approve a deal this autumn could be a less stable and predictable political entity. The fear is that this would play into the hands of May’s caution and Jeremy Corbyn’s anti-EU instincts.

In his Paris speech, Soros rightly argued that Europe and Britain had a common interest in a reformed EU. Such a Europe would distinguish better the EU and the eurozone, by making clear that EU membership can be explicitly multi-track and does not entail joining the eurozone. It would acknowledge that current eurozone rules must be changed and loosened.

The problem with this vision of Europe is not that it would not work. It would almost certainly work far better than the present version, and would potentially draw some of the sting of nationalist movements around Europe, and make Europe more attractive in Britain. The problem is that it is not seriously on offer. A multi-track Europe was precisely what David Cameron sought to secure in his 2015-16 negotiations. He didn’t get it. That rejection was followed by Brexit.

Yet these may be times for Europe to take a big gamble. It has to change to survive. Time and tide do not bring about change by themselves. Change happens when time and tide are seized by political leaders who know what change to make. In the era of May and Corbyn, it is hard to see who such British leaders might be. But the opportunity is opening, and the time is now.

• Martin Kettle is a Guardian columnist