On his first full day in office, British Prime Minister Boris Johnson urged the European Union on Thursday to rethink its refusal to renegotiate the Brexit deal, setting himself on a twin-track collision course — with the bloc and his own lawmakers — over his vow to leave the EU by Oct. 31.

Labour Party Leader Jeremy Corbyn: “Our country does not need arm-waving bluster but competence, seriousness and, after a decade of division policies for the few, to focus on the interests of the many.”

Johnson pledged to deliver Brexit and a “broader and bolder future,” as he addressed a rowdy session of Parliament.

He was heckled loudly by an opposition determined to thwart him, with Labour Party leader Jeremy Corbyn dismissing Johnson’s “arm-waving bluster.” The EU’s Brexit chief called Johnson’s speech “combative” and his demands unacceptable.

Johnson, who took office on Wednesday after winning a Conservative Party leadership contest, has less than 100 days to make good on his promise to deliver Brexit by Oct. 31. And Thursday’s session of Parliament was the last before a six-week summer break.

Rejecting the Brexit withdrawal agreement negotiated by his predecessor Theresa May, Johnson insisted that while he wanted a deal, it could only happen if the EU budged, especially on an insurance policy for the Irish border that has been rejected by U.K. lawmakers.

“I hope that the EU will be equally ready and that they will rethink their current refusal to make any changes to the Withdrawal Agreement,” he told Parliament during the 2½-hour session. “If they do not, we will, of course, have to leave — the U.K. — without an agreement.”

Johnson later spoke by phone to European Commission President Jean-Claude Juncker, who once again repeated the bloc’s insistence that it will not renegotiate the agreement on departure terms that it struck with May.

Juncker told Johnson that “the withdrawal agreement is the best and only agreement possible” but the EU was ready “to analyze any ideas put forward by the United Kingdom, providing they are compatible with the withdrawal agreement.”

The exchange was disclosed by an EU official who asked not to be identified because of the confidentiality of the phone call.

Chief EU Brexit negotiator Michel Barnier said Johnson’s “rather combative” speech was part of the British leader’s attempt “to heap pressure on the unity” of the bloc.

In a message to the 27 remaining member states, he said the EU must “be ready for all scenarios.”

Without a divorce deal, Britain faces a chaotic Brexit that economists warn would disrupt trade by imposing tariffs and customs checks between Britain and the bloc. They say that could send the value of the pound plummeting and plunge the U.K. into recession.

Nonetheless Johnson has vowed to complete Brexit and silence “the doubters, the doomsters, the gloomsters” who believe it can’t be done.

But details remain scarce about how Johnson’s government would alleviate the economic shock if Britain crashed out of the EU’s huge free-trading bloc, ripping up decades of agreements regulating everything from aviation to drugs to telecommunications.

He said he was ready to talk to EU leaders “whenever they are ready to do so,” and also promised to “turbo-charge” planning for a no-deal exit, with millions more allocated to a public information campaign for citizens and businesses.

He also repeated his threat to withhold the exit payment of 39 billion pounds ($49 billion) that May agreed to if there is no deal.

Since taking office Wednesday, Johnson has replaced many of May’s ministers with his own hand-picked Cabinet of loyal Brexiteers, and it met for the first time on Thursday. Many of them worked with Johnson in the 2016 referendum campaign to leave the EU, as did much of Johnson’s new backroom staff.

Despite the new lineup, Johnson faces the same problems that bedeviled May: heading a government without a parliamentary majority and with most lawmakers opposed to leaving the EU without a divorce deal.

Lawmakers who oppose a no-deal Brexit — including some of the Conservative ministers in May’s government who were swept away by Johnson — are vowing to put up a fight when Parliament returns from its break in September.

“This House will stop the prime minister,” said Scottish National Party lawmaker Ian Blackford, who branded a no-deal Brexit “economic madness.”

It’s almost certain that opposition lawmakers will try to topple Johnson’s government in a vote of no-confidence in September. There also is rising speculation that Johnson could call an early fall election in hopes of gaining a majority in Parliament for his plans.

The country’s next scheduled election is not until 2022, and Johnson says his priority is Brexit, not an early poll — but he hasn’t ruled one out.

In the meantime, Johnson must prove he can deliver on his optimistic pronouncements.

In a packed and testy session of Parliament on the hottest day of the year, dozens of lawmakers grilled him on details: How would he uphold the government’s promise to keep the border between Northern Ireland and EU member Ireland free of customs checks? How would he enforce his promise that all 3 million EU citizens living in Britain can stay?

He batted them all away, offering instead the blustering optimism that have made him one of Britain’s most divisive politicians.

As he boomed above the cheers and jeers, Johnson’s delivery had an echo of his idol, Winston Churchill. But instead of the wartime leader’s vow to give “blood, toil, tears and sweat,” Johnson promised “positive thinking and a can-do attitude.”

“There is every chance that in 2050 … we will be able to look back on this extraordinary period as the start of a new golden age for our United Kingdom,” he said.

Corbyn, leader of the main opposition Labour Party, said the country was worried that “the new prime minister overestimates himself.”

“He says he has pluck, nerve and ambition,” Corbyn said. “Our country does not need arm-waving bluster but competence, seriousness and, after a decade of division policies for the few, to focus on the interests of the many.”

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