The Liberal Democrats would extend free school meals to all primary schoolchildren, starting with those in poverty, Ed Davey has said in a challenge to Labour to match the pledge. Speaking in his first newspaper interview of the general election campaign, the Lib Dem leader announced a manifesto policy aimed at nearly 1 million more children living in poverty in England and their families. The £500m cost of the pledge would be paid by introducing a 4% share buyback tax modelled on the one brought in by the US president, Joe Biden, which the Liberal Democrats estimate would raise £1.4bn. At present the government only provides meals to children in reception, year 1 and year 2, and to children who meet family income conditions in year 3 and above. The Child Poverty Action group estimates that 900,000 children living in poverty – a third of school-age children in England – miss out on free school meals. “We think the case for it is overwhelming,” Davey said in his interview from the West Country, where his party is targeting a swathe of Conservative-held seats. “The Liberal Democrats are very progressive politicians. That’s who we always have been. It’s who we are. We believe in social justice … If we can get some Liberal Democrat MPs in the next parliament, many more of them, these are the things we’ll provide for.” Davey rounded off the first week on the general election trail on Thursday by careening down a water slide in Somerset. His approach to campaigning so far has been to engage in a series of stunts including falling off a paddleboard in Windermere and cycling down a steep hill in the Welsh town of Knighton. The resulting footage and pictures have garnered significant media attention for the party, which had 15 MPs when parliament was dissolved and is polling in third place on about 9%. Davey hopes to pull off a similar feat to 1997 when the Liberal Democrats under Paddy Ashdown increased their number of seats from 18 to 46. Davey would not commit to a target number of seats but said: “This looks to me like a once-in-a-generation election, a bit like 1997 … This is a moment for progressives to seize.” He said that behind the stunts was a party with serious and bold proposals in policy areas such as education, health and social care. The Lib Dems are pitching themselves as an alternative to Labour for progressives who want to get the Tories out. Asked once again whether he would rule out going into a coalition with the Conservatives in July, Davey said: “100%.” But he would not rule out a coalition with Keir Starmer’s Labour. “I’m not talking about anything beyond what I’ve just said on the Tories for the simple reason that I want to campaign on Liberal Democrat policies … I think it was right that we’ve made it very clear that the Conservatives are anathema to us. I’ve fought the Tories all my life, I fight them every day.” On which high-profile Conservatives he would like to see his party defeat, Davey named three: the chancellor, Jeremy Hunt; the education secretary, Gillian Keegan; and the justice secretary, Alex Chalk. Davey refused to set his conditions for propping up a Labour government in the event of a hung parliament, whether in a coalition or looser confidence-and-supply arrangement, though he said electoral reform had always been a Lib Dem priority. He said he had not spoken privately to Starmer since before the campaign began. “I sat next to him during the king’s coronation,” he said. “We compared notes – and we talked about football as well. As you know he’s an Arsenal fan, I’m a Notts County fan … I think he probably knows more about football than I do, let me be very, very honest. I’ve always followed football but he plays it.” Some question what differentiates Davey from Starmer. When asked this, he finds it easier to detail things they have in common. “There are things in his life which he had to struggle with and I’ve had quite a few in mine. There are actually more similarities in terms of our upbringing. We’ve had challenges to face,” he said. Davey has been a carer for most of his life – first for his mother who became terminally ill when he was a child, then for his grandmother and now for his son John, who is disabled. He feels an affinity with Starmer, who has spoken about his mother’s struggle with Still’s disease. When the general election was called, Davey and his daughter Ellie had been due to join the rest of their family in Budapest, where John regularly visits a specialist institute for neurological conditions. Instead, Davey’s brother stepped in to take Ellie to Hungary so Davey could start campaigning. The family returned home this weekend after two weeks away. “I’m very excited. It’s the longest time I’ve been away from my wife since we got married and my son since he was born,” Davey said. Besides a couple of constituency commitments, he will be taking a break from the campaign trail for a family weekend.