The co-leader of the Green party, Jonathan Bartley, has issued an invitation to the Labour leader to discuss a progressive alliance on left-of-centre politics, after a record showing in last week’s local elections. Bartley told the Guardian: “I’m saying to Keir Starmer: my door is open. You have my number – give me a call.” The Greens entered a pact with the Liberal Democrats and Plaid Cymru at the last general election in 2019, covering 60 seats, to avoid splitting the anti-Brexit vote. The Green party increased its share of the vote in that election, to more than 850,000 votes, though without winning any more seats in parliament. There is currently only one Green MP, Caroline Lucas in Brighton Pavilion. Bartley believes some form of wider alliance with Labour at the next general election could prove beneficial for a “progressive alliance”, an idea some experts think may be the best or perhaps only way to counter a surging Tory party. “We have been governing with Labour and the Lib Dems in councils; we have reached out to Labour. The ball is in the court of the Labour party – we are always ready to talk,” he told the Guardian in an interview. “Will Labour ever be able to form a government on its own? That’s a legitimate question to ask.” Any formal coordination would require the approval of Green party members. Bartley said: “The first step is to talk. We have not even reached that stage yet.” Sources in the Labour party have suggested that the party has not definitively ruled out the idea of some form of cooperation in future, but nor is it under active consideration at present. The Green party made a net gain of 91 council seats in the local elections, taking its national total to a record 444. It has a role in running 18 councils, including Brighton and Hove which it controls and Bristol where it is equal with Labour, with the possibility of more as hung councils work out compromises in the coming weeks. The party took seats almost equally from the Conservatives and Labour: 45 of its seats were won from Tory incumbents and 49 from Labour, with a further four coming from the Liberal Democrats. That shows, according to Bartley, that the Greens can win seats that Labour could not. “A vote for the Green party is a vote for the Green party,” he said. Bartley attributed the party’s stronger showing to increasing concerns over its core issues, of the climate crisis and the ecological emergency, and to changes in political outlook resulting from the Covid-19 pandemic. The party was ridiculed in some quarters for suggesting at the 2019 election that £100bn a year should be spent on building a zero carbon economy in the UK, as critics said such sums were unrealistic. However, such massive government intervention in the economy is no longer unthinkable, according to Bartley, as the response to the pandemic has shown. “The government is spending £300bn to £400bn in one year, and paying the wages of millions of people on furlough. So people understand now that what we were told about the economy was not right. It is possible to spend in an emergency,” he said. Bartley also believes Boris Johnson is missing the opportunity to rebuild the UK’s economy along green lines, following the shock of Covid-19. For instance, millions of people working from home instead of commuting could have a profound impact in reducing future greenhouse gas emissions, if people are helped to continue working from home where possible and if the government invests in amenities such as cycle routes and “15-minute” towns and cities, where people can access basic services from GPs to shops without needing a car. But Bartley fears the opportunity will be lost as the Conservatives focus on returning people to “normal” instead of helping to create a permanent and beneficial change. “There is no coherent transport policy,” he said. “There wasn’t one before the pandemic and there isn’t one now.” He pointed to government spending of £27bn on new roads, and £12bn in fossil fuel subsidies, and the axing of the green homes grant for insulation and low-carbon heating, as examples of the government’s failure to put in place a “green recovery” from Covid-19, despite Johnson’s rhetoric. The Green party wants a land value tax that would stop property developers sitting on land banks rather than building new homes, and wants higher standards to make sure all new homes are low-carbon, so they do not need costly retrofits in future. The UK will host vital UN climate talks, called Cop26, this November in Glasgow. Bartley said the prime minister would attract international criticism if he failed to start matching his green words with action. “An objective observer would say that Boris Johnson looks ridiculous, he’s a national embarrassment at the moment,” he said. “This should be a time to stand up and show leadership [on shifting to a low-carbon future], but he is saying one thing and doing another. He needs to come up with policies that show the UK is serious.”