In allowing his country to leave the EU, David Cameron has brought his career to a shuddering halt

There is little doubt that it will be a Brexiteer that succeeds Cameron as Conservative leader and Prime Minister. Boris Johnson will start as the clear front-runner, with Michael Gove tipped to become his Chancellor

David Cameron talks with suppoters at a campaign event for Britain Stronger In Europe (AFP/Getty)

David Cameron knows that his political epitaph will be as “the man who took us out of the EU”. Nothing else he has done matters, because it was he who took the reckless gamble that changed the course of Britain’s history.

Announcing his dramatic decision to stand down as Prime Minister only four hours after losing the EU referendum, an emotional Cameron listed the achievements of his six years in power – repairing the economy, boosting life chances and bringing in gay marriage. But the man who told his party to “stop banging on about Europe” will be remembered as the leader who put Europe centre stage and ended his own career by doing so.

The new Conservative leader, who will be in place by the start of the Tory conference in October, may be tempted to call an early general election to secure his or her own mandate – especially as the Tories are confident they would beat a Labour Party led by Jeremy Corbyn. The new PM will also be aware that Gordon Brown missed such a golden opportunity to win a general election when he succeeded Tony Blair in 2007.

Boris Johnson, Cameron’s long-term rival and friend in that order, will start the clear front-runner to succeed him. It is highly likely that the new leader will be a Brexiter. Michael Gove, the other figurehead of the Vote Leave campaign, is tipped to become his Chancellor unless he decides to run himself. Theresa May, the Home Secretary, who backed Remain but kept a low profile during the campaign, may emerge as the “Stop Boris” candidate. Others may enter a Tory race that is often won by an outsider – among them Margaret Thatcher, John Major, William Hague, Iain Duncan Smith and Cameron himself 11 years ago.

Cameron, saying he was not the right captain to steer the ship of state to its next destination, and was graceful enough to take responsibility for his fateful decision to call a referendum. He backtracked on two statements made in the campaign, saying that Britain could survive outside the EU and that he would not immediately trigger formal talks on the exit terms after a vote to leave.

It was an accidental Brexit. Cameron believed the festering issue of our EU membership had to be resolved sooner or later. But he didn’t need to call the referendum. It was an exercise in Conservative Party management – and to keep Ukip at bay at last year’s general election – rather than a response to any public demand for a referendum. George Osborne will also pay the price of Brexit. He was once Cameron’s heir apparent but might not even enter the leadership race now. Osborne is said to have expressed fears that a referendum would be a risky and unpredictable event. How right that was. Perhaps Cameron secretly hoped he would never have to implement the pledge in the Tory election manifesto because he would still be in coalition with the Liberal Democrats after last year's election, and they would block the referendum.

In the past two months, Cameron tried to re-run two previous campaigns in which he also had his back to the wall – the 2014 referendum on Scottish independence and the general election. He relaunched “project fear” on the economy. He rolled up his sleeves at campaign rallies to inject some passion. He used Downing Street’s negotiating power to ration his appearances in the TV debates. It worked in Scotland and at the election. But it didn’t work this time. The "essay crisis Prime Minister" failed.

As he did at the election, Cameron will have discussed with his senior aides two alternative statements to be made after the result. He had hoped to use the one written for a Remain vote but as the results came in last night, it became increasingly clear that he would have to use the Leave version when he spoke outside Downing Street this morning.

Cameron knew he could not survive for long after such a devastating blow to his authority. He was magnanimous in defeat and sees it as his duty to provide some stability in the next three months amid the turmoil on the financial markets.

Some 84 signed a pre-cooked letter saying that Cameron has a duty to stay on, including Johnson and Gove, an insurance policy encouraged by Number 10. But it only provided short-term cover and Cameron has jumped – honourably – before his impatient MPs started to push him out. They were never going to allow the man who negotiated a flimsy deal on Britain’s EU membership terms and failed to persuade the country to back it, to lead the talks on our exit terms.

It was also be untenable for the leader who said that Brexit would be “putting a bomb under our economy” to stay at the helm for very long. If Cameron had tried to hang on for any length of time, his backbenchers would have demanded he spelt out his departure timetable.

What remains of Cameron’s authority will now drain very quickly, as Blair found when he announced his departure timetable under pressure from Brown’s supporters.

Cameron bowed to the inevitable by leaving to the next PM the decision on whether to invoke Article 50 of the EU’s Treaty of Lisbon – which sets the clock running on two years of negotiations when a member state decides to leave the club. The Leave camp is in no hurry. Johnson and Gove favour informal talks with other EU countries and wants to delay formal negotiations that would put the EU in the driving seat -– possibly until after the French and German elections next year. Cameron will formally report the referendum decision at an already scheduled meeting of the 28 EU leaders in Brussels next Tuesday.

Some EU officials, fearing that Brexit could be the catalyst for the collapse of the entire EU project, might want to consider further concessions to the UK which could be put to a second referendum. Other EU figures will want a quickie divorce from their awkward partner – and might take legal action to force the start of formal negotiations if Britain plays for time.

A second referendum has been floated previously by Johnson but would be a dangerous move unless the UK won curbs on freedom of movement to answer public fears about immigration. Some 478 MPs declared for Remain and 159 for Leave, so the Commons could try to keep the UK in the single market, even though Vote Leave rejected the idea. Politicians will be very wary of appearing to defy the voters’ decision, which would only alienate the public even further from their political leaders.

Instead of planning his Cabinet reshuffle after winning the referendum, the man who won a surprise general election victory only 13 months ago has decided to reshuffle himself. His political career has been brought to a shuddering halt by a catastrophic misjudgement of his own making. What he called "the sweetest victory of all" last year has become the most bitter defeat.