Justice Secretary Michael Gove is pitching to be the prime minister to take Britain out of the EU, a day after he destroyed the chances of another frontrunner in what some colleagues called an act of treachery.
Gove's decision on Thursday to throw his hat in the ring to replace David Cameron, who is standing down after Britons voted to leave the European Union last week, upturned British politics after he had previously said he would back Boris Johnson.
His comment that Johnson, with whom he had campaigned across the country to secure the vote for Brexit, was not fit to lead effectively ended the popular former London mayor's hopes.
Five candidates are now hoping to replace Cameron, with interior minister Theresa May the favourite with bookmakers.
Ruling Conservative Party politicians will whittle the field down to two, before a final decision is made by party members with the new leader in place in early September.
The decision to quit the EU has cost Britain its top credit rating, pushed the pound to its lowest level against the dollar since the mid-1980s and wiped a record $US3 trillion ($A4 trillion) off global shares.
EU leaders are scrambling to prevent further unravelling of a bloc that helped guarantee peace in post-war Europe.
"I have to say I never thought I'd ever be in this position. I did not want it, indeed I did almost everything not to be a candidate for the leadership of this party," Gove said in a speech in central London as he launched his campaign.
Colleagues in the ruling Conservative Party who backed Johnson have poured oppobrium on Gove.
Johnson himself hinted he saw it as treason, hiding a quote from Shakespeare's play about political murder,"Julius Caesar, in his speech announcing his decision not to stand on Thursday.
Britain's biggest-selling tabloid the Sun said Johnson had been "Brexecuted".
Attempting to reach out to his party, Gove said he was driven by conviction and not ambition, and he had concluded Johnson was not the right man for the top job.
