The UK is ushering in a new era Wednesday as Boris Johnson enters 10 Downing St. with a promise to deliver Brexit by Oct. 31 with a government touted as a “cabinet for modern Britain.”

The brash former mayor of London and foreign secretary is replacing Theresa May, who announced her resignation last month after Parliament rejected the withdrawal agreement she reached with the European Union.

For the final time, May attended the weekly prime minister’s questions period in the House of Commons, where she defended her record and said she boosted jobs.

She said politics is “about the difference we make every day to the lives of people up and down this country.”

“Following my duties in the House this afternoon, I shall have an audience with Her Majesty the Queen. I shall then continue with my duties in the House, from the backbenches,” she said in response to the traditional first question about her agenda for the day.

An opposition MP asked May how she feels handing the reins over to a man who will “sell our country out to Donald Trump and his friends.”

Eliciting chuckles, she said she was “pleased” to hand things over to Johnson, who quit her cabinet in protest over her Brexit strategy.

Labour leader Jeremy Corbyn paid tribute to May’s “respect for public service,” but slammed her record on the economy, homelessness and Brexit.

He asked whether she would consider joining him “in opposing the reckless plans of her successor.”

After listing what she felt were her accomplishments, she said: “At its heart, politics isn’t about exchanges across these despatch boxes, nor about eloquent speeches or media headlines.

“It is about the difference we make every day to the lives of people up and down this country.”

After saying goodbye to her staff, May will travel the mile to Buckingham Palace to resign and ask Queen Elizabeth II to invite Johnson to form a new government.

The 93-year-old monarch will then meet Johnson — the 14th prime minister of her 67-year reign — before he stands outside 10 Downing St. to address the nation.

Johnson’s office said his government would be a “cabinet for modern Britain” with more women and a record number of ministers from ethnic minorities — a sign that he hopes to move beyond the largely white, male and Conservative members who chose him as their leader.

He promised in a victory speech Tuesday to deliver Brexit “in a new spirit of can-do.”

“I say to all the doubters: ‘Dude, we are going to energize the country, we are going to get Brexit done,'” he said.

With Post wires