Jeremy Corbyn has pledged to pull off another general election upset and recover from poor polling to deny Boris Johnson a return to Downing Street, as he effectively kicked off Labour’s campaign with a so-called alternative Queen’s speech setting out key policies.

Speaking to party activists in Northampton, where both parliamentary seats are held by Conservative MPs with tiny majorities over Labour – Corbyn reeled off a list of plans in areas including Brexit, inequality, education, the NHS, housing, crime and the climate emergency.

He said it was “the most transformative, radical and exciting programme ever put before the British electorate”.

Answering questions from reporters afterwards, Corbyn declined to comment on surveys that put the party’s support at as little as 25%, insisting he never looked at polling. But he did predict a similar upset to that of 2017 when Labour confounded the polls to deny Theresa May a majority.

Corbyn ignored a separate question about whether he would step down if he did not win the election.

In his speech he said Labour was seeking a radical transformation of the UK so that young people could “look forwards to the future with hope”.

“It’s not easy, I get all of that,” he said. “But the one thing this country can’t afford is the level of inequality that we have.”

He said that when an election was called, Labour would mobilise hundreds of thousands of supporters to push its message.

“That atmosphere and that message that things can and will be done very differently. Do we want our country run by a party that has cut, sliced, diced and privatised our public services, or do we want the ambition, enthusiasm and imagination of the Labour party to create that different and better society?”

To cheers from the crowd, he concluded: “I’ll take that message out there. I’m very fit, I’m very healthy, I’m very happy, and I’m very, very determined.”

Corbyn brushed off a suggestion that the party should be pushing for a second EU referendum before an election.

“A second referendum is what we propose under a Labour government, which would be, as I have said, not a choice between a no-deal cliff edge but between an intelligent arrangement with the European Union and remain.”

Many Labour MPs are worried about going into a general election at a time when the party is trailing badly in the polls, and they would rather see the issue of Brexit put to bed, allowing them to campaign on domestic issues.

Corbyn dismissed the planned Queen’s speech by the government as a “cynical stunt”, saying it was “full pomp and ceremony, setting out an agenda to parliament that it has no intention and no means of delivering”.

The rest of his speech was largely a list of previously announced Labour policies, including its plans for a so-called green new deal, reshaping the economy towards skilled, sustainable jobs.

Asked about the ongoing Extinction Rebellion protests in London, which Johnson and several government ministers have condemned, Corbyn praised the movement, predicting its leaders could even one day be commemorated on postage stamps, as earlier activists have been.

“Their right to protest has to be upheld, that is what our democratic rights are all about,” he said. “Obviously protests must be conducted in a peaceful way, and every time anyone condemns people for protesting they should think for a moment where protest can lead.”

He added: “Those women who stood up for the right for women to vote, the suffragettes, were condemned mercilessly by almost every newspaper in the country. They’re now on postage stamps.”

Asked about the case of a US diplomat’s wife who left the UK after being sought in connection with a fatal road crash, Corbyn said the US should take action to return her.

“I am alarmed and very concerned about that,” he said. “For somebody to be killed in our country and for the person who did it then to flee to the United States and then to claim diplomatic immunity is completely unacceptable.”

He condemned comments by Donald Trump that US citizens sometimes drove on the wrong side of the road in the UK. “I just think that’s the most crass, insensitive comment that anyone could ever make,” Corbyn said.