Speaking outside his Downing Street office after being formally appointed, Mr. Johnson — one of the key figures behind the 2016 Brexit referendum — promised to do a “new deal” with Brussels.

Newly-installed British Prime Minister Boris Johnson on July 24 promised to deliver Brexit on October 31 “no ifs, no buts” and prove wrong “the doubters, the doomsters, the gloomsters”.

Speaking outside his Downing Street office after being formally appointed, Mr. Johnson — one of the key figures behind the 2016 Brexit referendum — promised to do a “new deal” with Brussels.

A day after winning the leadership of his Conservative party, the former London mayor formally replaced Theresa May.

His ascent is the culmination of a lifelong ambition for the blond-haired politician, who delights in playing the clown but now faces an immense challenge ahead.

Mr. Johnson has promised to deliver Brexit in three months’ time but faces opposition in Brussels and has only a wafer-thin majority in the British parliament.

Beloved by many for his refusal to take life too seriously, he is accused by others of divisive rhetoric, a flexible approach to the truth and incompetence. Before he even took office, several pro-European ministers quit in protest at his threat to leave the EU without a divorce agreement to ease the split.

Opposition Labour leader Jeremy Corbyn challenged Mr. Johnson to call a snap general election, saying he has no mandate from the public to govern.

Although he won a landslide of Conservative party members, a YouGov survey on July 24 found Mr. Johnson’s approval rating was just 31% among the public.

Even his appointment was disrupted by climate protesters, who briefly stopped his convoy heading to Buckingham Palace to be nominated by Queen Elizabeth II.