Young people concerned about the climate crisis and air pollution are urging the London mayor, Sadiq Khan, to abandon his plans for a new four-lane road tunnel under the Thames or risk losing their support. Climate justice campaigners, anti-pollution activists and key youth groups inside the Labour party say Khan, who is standing for re-election on Thursday, is ignoring climate scientists, economists and health experts by pressing ahead with the £2bn Silvertown tunnel scheme in east London. They warn that unless he cancels the plans he, and the Labour party, could lose the backing of a generation of young voters. Anjali Raman-Middleton, a co-founder of the Choked Up anti-pollution campaign set up by a group who describe themselves as “black and brown teenagers from south London”, said: “It is becoming a real issue. The tunnel risks losing support from younger generations because it is us that will have to live with the consequences of this decision for years to come … It makes us feel like we have no one to vote for who really gets this stuff and is prepared to act. Gaya Sriskanthan, the co-chair of Momentum, the grassroots Labour campaign group, said the UK would struggle to meet its climate targets if “fossil fuel infrastructure” like the Silvertown tunnel went ahead. “Over and over again we’ve seen politicians paying lip service to the climate emergency, signing up to targets on paper, but failing to act when it really counts,” she said. “Failures like this will make young voters lose hope in Labour when it should be the party leading on climate action.” The tunnel would be built near the existing Blackwall tunnel in east London and would carry four lanes of traffic – two in either direction. Last year, the Guardian revealed the project could cost nearly £2bn over the next three decades if it goes ahead. Khan’s administration has repeatedly defended the scheme, saying it is essential to improve river crossings in east London – particularly the Blackwall tunnel – that are “antiquated and worn out” and claims the tunnel would alleviate pollution. The plans have faced opposition from a growing list of MPs, councillors, environmentalists, health experts and residents. They say it will increase pollution, drive up car use and increase emissions in one of the most deprived and polluted parts of the capital for years to come – all as the climate crisis accelerates. The shadow climate change minister, Matthew Pennycook, whose Greenwich and Woolwich constituency would contain one end of the tunnel, called on Khan to reverse the plan. Lyn Brown, the Labour MP for West Ham, where the other end of the tunnel would be, has also called for the project to be scrapped. At least eight constituency Labour party groups have also passed motions opposing the plans in recent months. Izzy Hickmet, from Labour for a Green New Deal, who grew up near the site of the proposed tunnel, said it would “cancel out much of the good work Sadiq has done for the environment since becoming mayor”. “There’s a clear choice here: between continued reliance on cars, and building the publicly owned, cheap, clean public transport we need to fight the climate emergency.” Hickmet added: “Unfortunately, this is part of a wider picture of Labour toning down its policies on the environment. This has led a significant number of young voters to turn away from the party - something which will only get worse if Sadiq Khan continues to back the Silvertown tunnel, ignoring expert opinion and widespread opposition within our party.” Last month, some of the UK’s leading climate scientists, economists and health experts signed an open letter calling for the scheme to be scrapped, saying it was incompatible with the UK’s legally binding climate targets and London’s own climate emergency declaration. “It would be foolhardy to press ahead with an infrastructure project that can only contribute to the UK’s excessive greenhouse gas emissions – as well as skewing London’s transport system further towards roads, and exacerbating local air pollution problems,” they wrote. A spokesperson for the Labour party defended the scheme, saying the existing Blackwall tunnel had “caused huge problems in central London for many years”. “The Silvertown tunnel is a project Sadiq inherited and has improved on and it is the only viable alternative to reduce the poor air quality and massive congestion caused in the area by the Blackwall tunnel.” They added the £2bn cost of the new tunnel would be met by charge a toll for using both the existing Blackwall and the new Silvertown tunnels. However, campaigners argue the mayor could toll the Blackwall tunnel, reducing congestion and air pollution, with the money raised spent on public transport and improved walking and cycling infrastructure rather than a new four-lane tunnel. Khan is ahead in the polls ahead of Thursday’s vote with his Conservative rival, Shaun Bailey, in second place. The Labour spokesperson described it as a “two-horse race” adding: “If you want a green mayor in City Hall then you must lend your vote to Sadiq Khan [or risk] waking up with a Tory mayor.” However, Raman-Middleton, from Choked-Up, warned Khan and Labour against taking young people for granted. “I think the Labour party is getting quite complacent. It thinks it can count on the youth vote but it won’t be able to if it keeps pushing policies like this,” she said.