Denis Staunton: How David Cameron gambled and lost

Dubbed the "essay crisis" prime minister for his record in averting disaster with a last-minute spurt of energy, David Cameron finally fell short on Friday and saw his premiership collapse because of a reckless gamble with Britain's constitutional future.

Time and again throughout his career, most notably in the Scottish independence referendum in 2014 and last year’s general election, Cameron had appeared to be heading for disaster only to snatch victory in the nick of time.

The pattern seemed to be repeating itself in the EU referendum, as the polls swerved towards Remain in the final days of campaigning after a scary couple of weeks when Leave was making the running. Voters were indeed moving towards Leave as the vote approached but the late surge was not enough to compensate for a huge number of postal votes, most of which were sent off a couple of weeks ago when support for Leave was at its highest.

It was a humiliating end to a premiership planned to resign at a time of his own choosing, some time before the end of the current parliament. Instead he found himself outside 10 Downing Street shortly after 8am on Friday, his wife Samantha standing close by and his voice cracking as he said Britain needed new leadership following the decision to leave the EU.

“Now the decision has been made to leave, we need to find the best way, and I will do everything I can to help. I love this country – and I feel honoured to have served it. And I will do everything I can in future to help this great country succeed,” he said.

Despite his privileged background, educated at Eton and married to a viscount's daughter, Cameron brought an air of relaxed normality to the Conservative leadership, following the awkward figures of Iain Duncan Smith and Michael Howard. Unencumbered with ideological baggage, the former public relations man succeeded in aligning his party with the attitudes of enough of the electorate to win a general election in 2010 for the first time in 13 years, although he had to share power with the Liberal Democrats.

Like many politicians, Cameron’s greatest strength was also his greatest weakness, however, and the ideological flexibility which was so useful in finding compromise also allowed him to cut corners and make injudicious promises.

He promised the referendum on Britain’s EU membership to protect his party’s right flank from Ukip, doubling down with a promise to reduce net immigration to the tens of thousands. The referendum was always a high-risk option but the promise to limit migration to a specific number, one Cameron could not keep, undermined his credibility.

This came to haunt him during the campaign, when the Leave side dismissed all Cameron's warnings about the consequences of Brexit as Project Fear. Because of the prime minister's diminished credibility, many voters were happy to ignore the Remain campaign's warnings.

"Its attempt to secure support through warnings of the economic consequences of leaving failed to move opinion in its favour, not least because they appeared rather overblown in the eyes of many voters. In contrast the Leave campaign had a simple and straightforward message, 'take control', that resonated strongly with many voters. It was a recipe for potential defeat – and in the event that was what happened," said John Curtice, senior fellow at UK in a changing Europe.

Until Friday, Cameron could boast that he had put Britain's economy back on a sound footing after the 2008 crash and saved the Union by keeping Scotland inside. Now, in the same way that Tony Blair's premiership is forever stained by the Iraq war, Cameron will be remembered as the man whose unnecessary gamble took Britain out of the European Union, left his country divided and could yet see the break-up of the United Kingdom.