Management books often repeat the dictum: ‘If there’s one thing worse than making mistakes, it’s not learning from them.’ So let’s apply that smug little idea to Brexit.

Before I start, a couple of housekeeping points. I voted Remain, but believe we must leave the EU and honour the referendum result. Second, as a former Brexit minister, writing this is a form of therapy for me.

Failure no. 1 — from which many other failures flow — was a lack of honesty. Brexit is the biggest challenge we’ve faced since 1939. It’s complex, existential and will take years. It demands a sense of national endeavour, of ‘let us go forward together’. One example of dishonesty was the much--repeated idea, which I had to trot out as a minister, that the whole thing would be completed by now, and we would enter an ‘implementation period’. This had the whiff of ‘the troops will be home by Christmas’. Not only is it impossible under Article 50 to negotiate the final relationship until the UK has left, but it was delusional to think we could do so in two years.

This brings us to failure no. 2: a lack of clarity. The core Brexit exam question is ‘What matters more: trade with the EU and access to their markets, or parliamentary control?’ Only when you have answered that can you define success and the options available to achieve your goal. Yes, white papers were published, but behind them lay fuzzy thinking. The opaque description for our objective was a ‘bespoke partnership’. Bespoke means tailored for the individual. To Remainers one could say: ‘Yes, Dominic, we will continue to have frictionless trade — suits you sir!’ To Brexiteers: ‘Don’t worry, Iain, we’ve seen the back of those EU judges — suits you sir!’

As 2016 slipped into 2017, and the pressure to trigger Article 50 grew greater, I consoled myself with the idea that the Prime Minister had created a top-secret war room in No. 10 where she sat like a Bond character, stroking the Downing Street cat, surrounded by a vast array of charts that detailed the moves she would take in the multi-dimensional chess that is Brexit. As time passed, it became obvious that no war room existed and that no one was even considering answering that core question (though the cat was real). And the reason is clear: answering the question would mean having to make a choice that might split the Conservative party in two.

Consequently, the ‘plan’ was built on sand. No real consensus was created early on as to what we wanted to achieve. And so here is failure no. 3: a lack of consensus meant that when the negotiations got tough, the Prime Minister could not count on the unequivocal support of her cabinet, still less the majority in parliament. Some were behind her — but many of them were clutching knives.

And that brings me to the negotiations themselves. I’ve always taken the view that the government had to be willing and able to walk away from the negotiations. To do that, we needed a Churchillian ‘Action This Day’ approach to preparations. Government had to be focused on getting the UK ready to fall back on WTO terms. Businesses had to be in the room, advising and helping. But for months, Brexit was treated as just another policy issue, not the existential change it is (failure 4). Worse, by losing its majority after the disastrous 2017 election (failure 5), the government could no longer count on parliamentary support for a ‘no deal’ outcome.

I could go on and on. There was the failure to reject the EU’s approach to negotiations, in which lay the trap of the Irish border; the failure to reject the concept of the backstop itself. While many of these failings could be put down to process, or the European schism that has divided the Conservatives for decades, the buck stops with No. 10. As they say in Sicily, it’s nothing personal, just business: but decency, resilience and patriotism are sadly insufficient when faced with the biggest challenge since 1939. Leaders lead — they don’t just manage.

And so, having said all this, in the spirit of bringing you solutions not just problems, here is what we need to learn from this mess.

If you believe we should honour the result of the referendum, then Brexit must, as I say, be treated as a national endeavour. The name-calling, the quest for unicorns in an ideologically pure Brexit, the appeals to overturn the result — all this has to give way to compromise, realism and consensus.

That means parliament must vote for the withdrawal agreement. It’s far from perfect — but the EU is not going to change it even if, via indicative votes, MPs can agree on the future shape of the EU/UK relationship. Consider the other options. There is no parliamentary majority for no deal. To revoke Article 50, or hold a referendum, would require a new government. So no deal, no Brexit, a referendum — all these roads lead to a general election. Parliament may demand that the price for supporting the withdrawal agreement is for the government to negotiate to join a customs union. If that happens, so be it. The point has come when red lines, manifesto commitments and party loyalty are trumped by the need for us to end the uncertainty and to leave the EU with a deal.

Once out, we need an entirely new approach to the next phase of the negotiations, which will decide the nature of our relationship with Europe. The government must build and maintain a consensus as to what it wants to achieve. Parliament must stand four-square behind the Prime Minister. To achieve that, given the parliamentary arithmetic, no options should be ruled out — including involving Labour MPs in the negotiating team.

Finally, the Prime Minister. The ship of state is heading fast towards the rocks. Chucking the captain overboard is unwise unless those on the bridge agree on who should take over, and what they should do. Clearly that’s not the case. But as soon as we are set on a new course that takes us out, Theresa May needs to depart.

One example of dishonesty, which I had to trot out as a minister, was that Brexit would be completed by now

George Bridges was a Brexit minister from 2016 to 2017.