Who saw Brexit coming? When David Cameron and Nick Clegg formed a coalition government 10 years ago, the idea of leaving the EU seemed a fringe concern, advocated by no leading elected politician. Just six years later, 52 per cent of British voters chose to leave.

Three people with a good claim to have predicted it first are Charles Grant, Denis MacShane and Patrick O’Flynn. Grant, the director of the Centre for European Reform, wrote in March 2005 about what would happen if Britain voted No in the referendum Tony Blair had promised.

“The what?” I can hear some people asking. Most people with better things to do with their time will have forgotten that one of several referendums Blair promised but didn’t hold was one on the EU constitution, a treaty drawn up in 2004 to adapt EU rules to its expanded membership, and to consolidate all the EU treaties into a single document.

The convention to draft the constitution, incidentally, was responsible for turning Gisela Stuart, the Labour MP for Birmingham Edgbaston, into a Eurosceptic. As a pro-EU Blairite loyalist, she was appointed by the prime minister as one of the UK’s representatives. By the time the constitution was finished, she opposed it, and 12 years later she was the leading Labour voice in the Vote Leave campaign.

Meanwhile, Blair surprised everyone by promising a referendum on the constitution before the UK ratified it. This was for the simple reason that he thought Michael Howard, the Tory leader, would gain votes in the 2005 election by advocating a referendum if Labour did not.

That should have been a clue, because, as Denis MacShane points out, Blair understood that, whatever the question in a referendum about Europe, the answer was likely to be “No”. MacShane, who was Europe minister at the time, says most of the press, the Tory leadership and “a block of Labour left-wingers like Jeremy Corbyn, as well as anti-EU veterans like Peter Shore, would have campaigned to defeat Blair”.

But Blair was also canny enough to realise that other countries were going to hold referendums first, and that one of them, probably the Czech Republic, was likely to kill the constitution without Britain needing to do so. As it turned out, the constitution didn’t even get that far. The voters in France rejected it, just after Blair was re-elected in May 2005, by 55 per cent.

That seemed to be that, and the constitution was quickly forgotten. After a tactical interval, some of its provisions — more majority voting and a new post of European Council president — were revived in the Lisbon Treaty. Most countries tactfully decided against putting the treaty to referendums. That seemed a cynical, if effective, way of avoiding trouble, but in the British case, all it did was postpone the reckoning.

Charles Grant was one of very few people who could see that clearly, if only because he thought through what would happen if Britain had held a referendum on the constitution and been the only country to reject it.

He assumed that Labour would win the 2005 election, but if it then lost the referendum, “the triumphant Eurosceptics would be demanding more”. He went on: “Having defeated the treaty, many of them would see ‘renegotiation’ as the obvious next step.”

Their demands would be “incompatible with EU membership”, he wrote, and “the public would, therefore, turn against the EU itself”. Ten years later, it came to pass.

The third person who saw it coming was Patrick O’Flynn, a friend and rival of mine who was chief political commentator for the Daily Express. He remembers a conversation with Matthew Elliott, the boss of the TaxPayers’ Alliance, in 2008.

The Liberal Democrats under Nick Clegg had just called for an in-out referendum because they thought that was the only referendum question they could win. “Matthew told me he thought a Leave campaign could win if the campaign was pitched correctly.