Prime Minister David Cameron may go down in history as the man who led Britain out of the European Union, with a strong chance that he will not survive the country's political earthquake.
As Britain voted to become the first state ever to withdraw from the bloc on Thursday (Jun 24), according to national media forecasts, Cameron's epitaph could be sealed after six years in power.
"He's put himself front and centre of the 'Remain' campaign, and to have lost the campaign would be a massive blow to his credibility," Tim Bale, professor of politics at Queen Mary University of London said earlier.
"We probably would, within a few days or weeks, see him signal his intention to go as soon as a leadership contest could be conducted," he told AFP.
Brexit brought to an end Cameron's winning run, having become prime minister in 2010, winning a referendum to keep Scotland in the United Kingdom in 2014 and securing a surprise outright victory for his Conservative Party in last year's general election.
Kenneth Clarke, a senior Conservative and former finance minister who wanted to stay in the EU, said Cameron "wouldn't last 30 seconds" if he lost the referendum.
However, 84 Conservative MPs who favoured Brexit offered an olive branch as the results emerged, telling Cameron in a joint letter that he had a "duty and a mandate" to lead the country, whatever the outcome.
If he accepts the offer, Cameron faces a huge battle to re-establish his authority after a bitter campaign that has divided his party.
He may not last long in any case as he has indicated that he would step down as prime minister before the 2020 election to make way for new blood.
SURPRISE WIN LED TO REFERENDUM
As the campaign took on an increasingly anti-establishment, anti-elite tone, the polished authority of Cameron, supported by big hitters from US President Barack Obama to the International Monetary Fund, struggled to cut through.
The son of a stockbroker, Cameron was educated at elite boarding school Eton and Oxford University, where he was admitted to the Bullingdon Club, a hard-drinking, socially exclusive student group.
He worked for the Conservatives as an advisor before a stint in public relations, which ended when he was elected to parliament in 2001.
Cameron rose swiftly through the ranks of the party -- which was then struggling badly against prime minister Tony Blair's Labour government -- and was elected leader in 2005 at the age of 39.
He tried to "detoxify" the party brand in part by avoiding discussion of the EU, which has split the Conservatives since Margaret Thatcher's premiership in the 1980s.
At the 2010 general election, Cameron became the youngest premier for 200 years but the centre-right Conservatives did not win enough seats to govern alone and had to form a coalition with the centrist Liberal Democrats.
The coalition was dominated by spending cuts as Britain emerged from recession, while foreign policy debate was largely hijacked by Conservative wrangling over the EU.
After five years in coalition, the Conservatives won a surprise clear majority in the May 2015 general election, allowing them to rule alone.
The win meant that the EU referendum -- first promised by Cameron in 2013 to placate his restive party, but which many in Westminster say he never believed would happen -- became a reality.
DESERTED BY ALLIES
Cameron spent much of the rest of 2015 lobbying other European countries for a deal to improve Britain's relations with the EU.
Sealed in February, this allowed him to argue going into the referendum that Britain had a "special status" in the 28-country bloc, notably allowing it to limit benefit payments to EU migrants.
But the deal was derided as "thin gruel" by some Conservative MPs.
And the bitterest blows to Cameron came as campaigning got under way.
Some of his most loyal lieutenants including justice minister Michael Gove -- godfather to one of Cameron's children -- said they would campaign for Brexit.
Then Boris Johnson, the former London mayor seen as a future successor to Cameron by many Conservatives, sprung a surprise by also backing "Leave".
During the campaign, Cameron led from the front with a barrage of speeches arguing that Britain's economy would be badly hit by Brexit.
However, he struggled to counter the "Leave" camp's argument that immigration from EU countries needed to be cut to reduce the strain on public services, and that this could only happen if Britain left.
There have been almost weekly newspaper reports about leadership coups in the event of an out vote, while polls suggest most Britons want Cameron to resign if he loses.
Ultimately, though, a change of prime minister might be seen as one of the less significant consequences for a country plunged into the unknown.