New U.K. Prime Minister Boris Johnson speaks to media outside 10 Downing Street | Jeff J Mitchell/Getty Images Boris Johnson pledges to leave the EU on October 31: ‘No ifs, no buts’ New prime minister gives first speech.

LONDON — Boris Johnson said the U.K. would leave the European Union "no ifs, no buts" on October 31 as he pledged to "restore trust in democracy."

Arriving at No. 10 Downing Street, the new U.K. prime minister pledged to strike a "new" and "better deal" which would maximize the opportunities of Brexit, claiming he had every confidence he would crack it in 99 days time.

He also called for a warm and close partnership with the EU, telling citizens of the bloc they would have the "absolute certainty of the right to live and remain [in the U.K.]"

Johnson also reiterated his threat that the U.K. could withhold the £39 billion Brexit settlement.

“Don’t forget that in the event of a no deal outcome we will have that extra lubrication of the £39 billions,” he said.

Johnson said it was vital to prepare for the “remote possibility” Brussels refuses to negotiate further, although he said he did not want that outcome.

Preparations “cannot be wasted,” he said. “That is because under any circumstances we will need to get ready at some point in the near future to come out of the EU customs union and out of regulatory control fully determined at last to take advantage of Brexit.”

“Whatever deal we do, we will prepare this autumn for an economic package to boost British business and to lengthen this country’s lead as the number one destination in this continent for overseas investment.”

Johnson also set out his domestic agenda including a pledge to put more police on the streets and to fix the social care crisis "once and for all."

The former London mayor won a ballot of Conservative Party members to be elected leader, announced on Tuesday, after promising to deliver Brexit by October 31.

Taking personal responsibility for delivering Brexit, he said "the buck stops here."

He spoke shortly after being invited to form a government by Queen Elizabeth II during an audience at Buckingham Palace.

"The time has come to act ... to take decisions, to give strong leadership and to change this country for the better. My job is to serve you, the people," he said.