By William James and Kylie MacLellan

LONDON (Reuters) – Boris Johnson used his first speech as prime minister to vow to lead Britain out of the European Union on Oct. 31 “no ifs or buts”, warning that if the European Union refused to negotiate then there would be a no-deal Brexit.

Johnson, who has been hailed by U.S. President Donald Trump as Britain’s Trump, is sending the strongest message yet to the EU that he will be taking a distinctly tougher approach to negotiating the Brexit divorce deal.

He enters Downing Street at one of the most perilous junctures in post-World War Two British history – the United Kingdom is divided over Brexit and weakened by the three-year political crisis that has gripped it since the 2016 referendum.

“We are going to fulfill the repeated promises of parliament to the people and come out of the EU on October 31, no ifs or buts,” Johnson, 55, said after arriving at his new residence, No.10 Downing Street.

“We can do a deal without checks at the Irish border,” Johnson said, watched by his girlfriend Carrie Symonds and his staff. “It is of course vital at the same time that we prepare for the remote possibility that Brussels refuses any further to negotiate and we are forced to come out with no deal.”

One of Britain’s most prominent Brexit campaigners, Johnson has repeatedly pledged to leave the EU by Oct. 31 – “do or die” – and to inject a new optimism and energy into the divorce, which he argues will bring a host of opportunities.

But his strategy sets the United Kingdom up for a showdown with the EU and thrusts it toward a potential constitutional crisis, or an election, at home.

“NEVER MIND THE BACKSTOP”

One of the issues that prevented his predecessor Theresa May getting a divorce deal through parliament was the Irish “backstop” – a provision that would maintain a customs union with the EU if no better solution was found.

Johnson was bullish, however. “Never mind the backstop. The buck stops here,” he said.

He said he would ensure “the people” were his boss and that he would accelerate preparations for a “no-deal” Brexit – a threat he intends to use to force a reluctant EU to renegotiate the exit deal it agreed with May but which parliament has rejected three times.

To implement Brexit, Johnson will appoint Dominic Cummings, the campaign director of the official Brexit Vote Leave campaign, as a senior adviser in Downing Street.

Earlier May, who had formally tendered her resignation to Queen Elizabeth, left Downing Street after a three-year premiership marred by crises over Brexit.

She appeared to be fighting back tears as she was applauded out of the House of Commons chamber.

Johnson had a possible foretaste of turmoil ahead when, as he drove to his audience with the queen, Greenpeace protesters tried – but failed – to block the path of his car as his chauffeur drove around them.

Now formally “Prime Minister and First Lord of the Treasury”, Johnson’ first task will be to appoint key members of the government – names that will give a hint of how he will handle Brexit, Britain’s most significant decision in decades.

BREXIT GOVERNMENT?

But ‘Prime Minister Johnson’ – a man known for his ambition, blond hair, flowery oratory and cursory command of detail – must solve a series of riddles if he is to succeed where May failed.

The 2016 Brexit referendum showed a United Kingdom divided about much more than the EU, and has fueled soul-searching about everything from secession and immigration to capitalism, the legacy of empire and modern Britishness.

The pound is weak, the economy at risk of recession, allies are in despair at the Brexit crisis and foes are testing Britain’s vulnerability.

Johnson’s Conservatives have no majority in parliament and so can only govern with the support of 10 lawmakers from the Brexit-backing Democratic Unionist Party in Northern Ireland.

While Johnson has said he does not want an early election, some lawmakers have vowed to thwart any attempt to leave the EU without a divorce deal. Nigel Farage, whose Brexit Party trounced the Conservatives in May’s EU elections, said he was open to an electoral pact with Johnson.

The appointment of Cummings, known for his campaign skills but also for a combative style that challenges the consensus, indicates Johnson is serious about going in hard on Brexit and wants a first-class political campaigner close.

Interior minister Sajid Javid is widely tipped to stay in a top job – possibly as finance minister – and was spotted flanking Johnson as he arrived to meet lawmakers.

A record number of ethnic minority politicians are expected to serve as ministers including Priti Patel, the former aid minister who resigned in 2017 over undisclosed meetings with Israeli officials, and current employment minister Alok Sharma.

Foreign Secretary Jeremy Hunt, Johnson’s rival for the leadership, was offered the job of defense minister but turned it down, Sky News TV reported.

NO DEAL?

A no-deal Brexit could also prompt Scottish nationalists, who want the UK to remain inside the EU, to seek a fresh referendum on Scottish independence.

Many investors say a no-deal Brexit would send shock waves through the world economy and tip the world’s fifth-largest economic power into recession, roil financial markets and potentially weaken London’s position as the pre-eminent international financial center, they say.

Brexit supporters say those fears are overblown and the United Kingdom will thrive if cut loose from the European project, which they cast as a German-dominated bloc that is falling far behind its global competitors such as the United States and China.

“If he really wants a ‘no-deal’, he will get it. We will never push an EU member out, but we can’t stop him,” one EU diplomat said. “More likely, his own parliament would.”

(Additional reporting by Elizabeth Piper, Andy Bruce, Kate Holton, William Schomberg, David Milliken and Paul Sandle in London and Gabriela Baczynska in Brussels; Writing by Guy Faulconbridge; Editing by Janet Lawrence and Kevin Liffey)