Boris Johnson has vowed to repay the trust of former Labour voters in north-east England who switched to the Conservative party in the election, during a visit to the region.

Johnson told new Tory MPs and local activists that they had changed the political landscape, the Conservative party and the country for the better, in a speech in Sedgefield, once the constituency of the former Labour prime minister Tony Blair.

Sedgefield was one of several former Labour heartland constituencies in the north-east and the Midlands to be taken by the Conservatives after they won an 80-seat majority in Thursday’s general election.

“I want to thank all the people of those incredible constituencies,” Johnson said on Saturday. “I want to thank all of you for the trust you have placed in the Conservative party and in me, and I know how difficult it was to make that decision.

“I want the people of the north-east to know that we in the Conservative party, and I, will repay your trust. Everything I do as your prime minister will be devoted to repaying that trust.

“First of all, what are we going to do? We are going to get Brexit done.”

Johnson spoke at a crowded Sedgefield cricket club. In a pantomime-style call and response, the prime minister ran through the Conservative party’s main manifesto promises, including the misleading pledges to build 40 new hospitals and recruit 50,000 more nurses, and to employ 20,000 police.

“What we want to do as Conservatives [is] we want to take our country forwards, but we want to do it by uniting and levelling up across the whole of the UK,” he said. This would be achieved by investing in infrastructure across the country and spreading opportunity.

He added: “Our country has now embarked on a wonderful adventure. We are going to recover our national self-confidence, our mojo, our self-belief.”

Speaking outside No 10 on Friday, Johnson had said he would “work round the clock” to repay the trust of those who had voted Conservative for the first time.

Play Video 4:38 Boris Johnson urges UK to 'let the healing begin' after divisive election – video

His comments were later echoed by Robert Jenrick, the housing secretary, who said the government planned to redirect investment towards those communities that felt they were not being heard.

“We are very grateful to these traditional Labour voters, in many cases, for lending us their support on this occasion, perhaps because of Brexit,” Jenrick told BBC’s Newsnight on Friday. “We need to earn that trust now and hopefully we will have five years ahead of us to do that.”

Earlier on Saturday, Paul Nowak, the deputy general secretary of the Trades Union Congress, said if Johnson wanted to retain the support of voters in the Midlands and north-east he needed to stand by promises to engage with the issues that motivated them.

Nowak urged Johnson to “put your money where your mouth is, engage with the unions, engage with working people” to get a Brexit deal that protected workers’ rights.

“You know, there are some contradictions in the prime minister’s position,” Nowak told BBC Radio 4’s Today programme. “He said, I think, before the election that he wants to protect and enhance employment rights, but if you look at that withdrawal bill, it delivers none of those protections.

“I think the government needs to now widen the conversation to include businesses, to include trade unions, to think about what this future relationship looks like.

“And I think our message clearly to Boris Johnson would be to put people before politics, to deliver a Brexit deal that does protect jobs and employment rights, and I think that means getting a right deal not just a quick deal. And I think it does mean standing by the commitments he’s made to those voters in the north-east and in the Midlands who may have voted for the first time.”

He added: “A deal that threatens jobs and people’s employment isn’t a deal that we can live with.”