Opponents of a new four-lane tunnel under the River Thames are making a last-ditch attempt to halt the £1.2bn scheme, which they say will be environmentally destructive and cripplingly expensive. Campaigners are to write to the oversight committee at the Greater London Authority asking it to urgently review the proposal. Victoria Rance, from the Stop Silvertown Tunnel Coalition, called on the London mayor, Sadiq Khan, to investment in river crossings for pedestrians, bicycles and cargo bikes instead of “locking in car use” for decades. She said the project was a “[Boris] Johnson era monstrosity” that undermined efforts to clean up the capital’s air as well as the mayor’s wider environmental targets – with dire consequences for some of the London’s most vulnerable citizens. “It is economically worthless and environmentally destructive,” she said. “It undermines his 2030 carbon neutrality target, and his goal of increasing cycling and walking – instead giving incentives to keep traffic levels high to pay off the scheme.” The tunnel will be funded with a loan that is due to be repaid by introducing tolls on both the Blackwall tunnel and the Silvertown scheme once it opens. Preliminary preparation work is due to start any day. Supporters say the tunnel, which would connect the Greenwich peninsula to west Silvertown, will ease congestion at Blackwall tunnel, provide better access to jobs and services, and improve the resilience of the road network in response to developments in Greenwich and the Royal Docks. A spokesperson for Sadiq Khan, the mayor of London, said: “A new tunnel at Silvertown is important as the existing infrastructure is both antiquated and worn out. The combination of introducing tolls on both the Blackwall tunnel and at Silvertown – and the extension of the Ultra Low Emission Zone from 2021 so that Silvertown will be within the area covered – will play a crucial role in tackling congestion, improving air quality and providing much-needed additional bus services across the river.” Campaigners dispute the claims. Rance said: “[The mayor] could achieve almost the same outcomes – six years earlier and without spending £1.2bn on a new tunnel – by tolling the Blackwall tunnel, now, to fully remove congestion.” The scheme comes as the mayor has unveiled a raft of new environmental measures, from declaring a climate emergency to setting a 2030 carbon neutral target. In response to the coronavirus, London has unveiled plans for one of the biggest walking and cycling zones of any capital city in the world to encourage people out of their cars. The spokesperson for the mayor said he remained committed to his environmental programme. “[Khan] has been clear that he doesn’t want to replace one health crisis with another, and he is determined that our city’s recovery from coronavirus will be clean, green and sustainable. “His bold London Streetspace plans will create one of the largest car-free zones in any capital city in the world, and are making it safer and more convenient for millions more journeys to be made on foot or by bike. Rance said pressing ahead with the tunnel in this context was unforgivable. She said growing evidence linking air pollution to coronavirus – and the higher death toll among ethnic minority groups – meant it was likely to take a disproportionate toll on those communities. “The mayor seems startlingly blind to the structural racism inherent in spending £1.2bn in imposing a scheme that will almost certainly increase traffic and pollution – and certainly lock in existing pollution levels into the future – through 80% black and minority ethnic Newham, which is already the most polluted borough in the UK.”