Brexit campaigner and former London mayor Boris Johnson announces that he won't run for prime minister, at a press conference in central London on June 30, 2016
London (AFP) - Leading Brexit campaigner Boris Johnson on Thursday ruled himself out of the race to succeed Prime Minister David Cameron in a bombshell announcement just a week after Britain voted to leave the EU.
The decision by the former London mayor upended the leadership contest in the ruling Conservative Party and added to the deep uncertainty over how and when Britain will split from the bloc.
The shock outcome of the June 23 referendum has led to massive political upheaval, with warnings about the country's economic future and fears about its unity as support for independence surged in pro-EU Scotland.
The maverick Johnson had been tipped as a favourite to succeed Cameron, who resigned after the vote saying he would leave it to his successor to begin formal talks with the EU on Britain's departure -- despite European leaders insisting on a quick divorce.
The frontrunner in the five-horse race is now interior minister Theresa May, who supported staying in the EU but insisted she would honour the referendum outcome and lead Britain out of the bloc.
In a boost to her fledgling campaign, the mass-selling Daily Mail newspaper endorsed her candidacy under the headline: "A party in flames and why it must be Theresa."
- 'Greatest constitutional crisis' -
Johnson made his announcement after fellow Brexit campaigner Michael Gove effectively torpedoed his chances by announcing his own surprise bid for the top job, sharply criticising his mop-haired ex-ally.
The power struggle brought comparisons to Shakespeare tragedies, with one MP likening Gove's actions to those of a murderous Macbeth.
Senior Conservative Michael Heseltine said Johnson -- author of a book on Britain's wartime leader Winston Churchill -- was "like a general, that led his army to the sound of guns, and at the sight of the battlefield abandoned the field."
He accused Johnson of generating "the greatest constitutional crisis of modern times".
After an 11-minute speech trumpeting his achievements as London mayor and outlining his vision for Britain, Johnson left the punchline for the end.
"Having consulted colleagues and in view of the circumstances in parliament, I've concluded that person cannot be me," he told shocked supporters.
He also appeared to quote some of the words spoken by Brutus before he killed Julius Caesar in the Shakespeare play -- quickly interpreted by political commentators as a reference to Gove's actions.
Observers were left stunned by the dizzying events in the corridors of power, where opposition Labour leader Jeremy Corbyn is clinging on to his job despite a mass revolt by his party's MPs.
The veteran socialist has been accused of not campaigning hard enough to stay in the EU, but insists he still has the support of party members.
- Central bank warning -
As the political drama played out, Bank of England governor Mark Carney warned about "heightened uncertainty" following the "Leave" campaign's victory.
Carney said the Brexit vote could increase unemployment and warned there were also "risks of adverse spillovers to the global economy".
He extended emergency liquidity loans for banks until September and hinted at possible interest rate cuts, sending the pound tumbling further against the euro.
"One uncomfortable truth is that there are limits to what the Bank of England can do," he added.
Sterling was at 83.8 pence per euro at 1515 GMT, surpassing the previous low reached in March 2014. It also slid to $1.3234 but was still up from the 31-year low of $1.3121 it touched on Monday.
But Carney's comments sparked a late-session flurry in London's benchmark FTSE 100 index of shares, which closed 2.3 percent higher. Shares in Paris and Frankfurt also rallied for a third straight day.
- 'Brexit means Brexit' -
Although she backed staying in the EU, May insisted "Brexit means Brexit".
"The campaign was fought, the vote was held, turnout was high and the public gave their verdict," she added.
The outcome, after an often acrimonious campaign, triggered anger among those who wanted to remain in the 28-member EU.
More than four million people have signed a petition calling for a second referendum.
But May said she would not trigger the formal process for leaving the EU known as Article 50 until next year, despite pressure from other European countries.
For his part, Gove said he would "not be dictated to on the timetable of the manner of the negotiations" and would only begin negotiations when it was "right for Britain".
The five leadership candidates will be whittled down to two by a series of ballots by Conservative MPs in the coming days before being put to a vote of party members.
The new leader will be announced on September 9, and will become prime minister with no need for a new election.