Mr Boris Johnson, the hardline Brexiter, is Britain's new prime minister, after a resounding victory yesterday in the Conservative Party leadership race to succeed Mrs Theresa May.
The former London mayor, always the favourite to beat Foreign Secretary Jeremy Hunt, garnered two-thirds of the votes.
Immediately after the results were announced, he promised to fulfil his "do or die" pledge to deliver Britain's departure from the European Union by Oct 31 and "take advantage of all the opportunities it will bring in a new spirit of 'can do' ". He added: "And we are once again going to believe in ourselves and what we can achieve."
The former foreign secretary said: "Like some slumbering giant, we are going to rise and ping off the guy-ropes of self-doubt and negativity.
"We are going to unite this amazing country and take it forward."
The divorce from the EU had been delayed three times.
Mr Johnson, 55, was a leading figure of the Brexit campaign, which won the referendum by a 52 per cent majority.
Yesterday, he captured the votes of 92,153 Conservative Party members, while his rival received 46,656. More than 87 per cent of the party's 160,000 members voted in the contest.
The eurosceptic officially enters Downing Street as the new prime minister at about 4pm local time (11pm Singapore time) today, after Mrs May holds her final Prime Minister's Questions session and then tenders her resignation before Queen Elizabeth II.
Mr Johnson is expected to form a new Cabinet by the evening.
He will face a sea of challenges as he inherits a party deeply divided on Brexit and a wafer-thin majority. The Tories need the backing of the Democratic Unionist Party to prop up its majority in Parliament.
He is almost certain to face the same Brexit impasse his predecessor did, given that the House has also blocked a no-deal Brexit.
He has vowed to renegotiate a deal with the EU, which has said repeatedly that the Withdrawal Agreement is not open for renegotiation.
His pledge to leave the bloc, deal or no deal, has left Britons worried as the country hurtles towards a tumultuous exit in about 100 days.
The sterling slipped 2 per cent against the US dollar this month as a no-deal Brexit became increasingly likely. The British currency is down 2.4 per cent since the start of the year, the Financial Times reported.
Several officeholders have quit or will do so before Mr Johnson takes office. They include Chancellor of the Exchequer Philip Hammond, Justice Secretary David Gauke and Junior Education Minister Anne Milton. On Monday, a junior foreign office minister resigned, and last week, the culture minister stepped down. More resignations could be on the cards.
Meanwhile, United States President Donald Trump congratulated Mr Johnson on Twitter, saying: "He will be great!"
On the enormity of the new leader's tasks, Professor Iain Begg of the London School of Economics and Political Science told The Straits Times: "He will struggle to reconcile conflicting views not only on what would be the best outcome for the UK, but also the mutually inconsistent promises he has been making to secure his victory... He is likely to have to renege on some core promises.
"That said, I still cling to the view that there is enough common sense in the British body politic to ensure that no-deal will not happen."
