The mayor of London is being urged to make an 11th hour intervention and halt plans for a new four-lane road tunnel under the River Thames that opponents say would worsen pollution and exacerbate the climate crisis. Tunnelling equipment is on site on the banks of the Thames, and work on the £2bn Silvertown tunnel is due to start in the coming weeks. But the scheme has faced widespread opposition from local people, politicians, climate scientists and medical experts who say it would increase traffic and worsen public health in some of the most deprived boroughs in the country. They also say it will lock in high carbon transport for generations to come. Siân Berry, a Green party member on the London assembly, said it was still not too late for Sadiq Khan to change his mind. “This is the mayor’s very last chance to stop this and save the majority of the project costs … if he stops the tunnelling machines now, he can avoid not only creating traffic and pollution across the wide area of London, but also avoid wasting money on a project that belongs in the last century.” Simon Pirani, an honorary professor at the University of Durham and member of the Stop Silvertown Tunnel campaign group, agreed: “It is still not too late to cancel this project, which will be so damaging and will exacerbate the local air pollution problems and undermine London’s efforts to meet its climate targets.” The tunnel is due to be built near the existing Blackwall tunnel in east London and would carry four lanes of traffic – two in each direction. The Guardian revealed the project could cost more than £2bn over the next three decades if it went ahead. Opponents privately acknowledge the chances of stopping the tunnelling at this stage are slim but say the fight is not over. Next week the Green party will hold a meeting asking for ideas about what the tunnel could be used for – if built – instead of private fossil fuel-based transport. Berry said Londoners were capable of coming up with many other options that could work, from new train and bus links to cycling and walking routes under the Thames. She said they may even want something completely different from the tunnel, such as an arts or music venue. “The mayor needs to hear absolutely clearly from us, if the tunnelling starts that is not the end of the opposition to this project. This is a scheme that simply cannot go ahead.” Advertisement The plans have faced opposition from a growing list of MPs and councillors. The shadow climate change minister, Matthew Pennycook, whose Greenwich and Woolwich constituency would contain one end of the tunnel, has 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 it to be scrapped. At least eight constituency Labour party groups have passed motions opposing the plans in recent months. Climate justice campaigners, anti-pollution activists and key youth groups inside the Labour party also oppose the scheme and warn that unless Khan cancels it he, and the Labour party, could lose the backing of a generation of young voters. Khan’s administration has repeatedly defended the scheme, claiming it is essential to improve river crossings in east London – particularly the Blackwall tunnel – that are “antiquated and worn out” and say it would alleviate pollution. A spokesperson highlighted that cross-river bus services would use the tunnel and added: “Both the Blackwall tunnel and new Silvertown tunnel will be subject to a user charge and, when combined with the mayor’s overall policy of reducing car use across Greater London in favour of active and public transport options, will help reduce congestion without increasing the volume of traffic crossing the river.”