Campaigners have hit back at National Highways’ ambition to make the Lower Thames Crossing the “greenest road ever” in the UK.

On Tuesday, a new target to reduce the multi-billion-pound project’s construction carbon emissions by 70% was announced.

However, the Transport Action Network (TAN) compared it to trying to put green lipstick on a pig.

If approved, the project would see a new road connect Kent and Essex through a tunnel beneath the River Thames in a bid to ease congestion in the Gravesend and Dartford area.

The 14.3-mile stretch of road would have a link off the M2, east of Gravesend, go under the Thames and emerge near Tilbury and then connect with the M25.

But TAN director Chris Todd believes the emissions from traffic generated by the new road would be “much greater than the potential savings from slightly less polluting construction”.

He said: “National Highways is making ever more desperate attempts to keep this doomed scheme afloat.

“The Chancellor’s admission she cannot pay for the Lower Thames Crossing and that the private sector needs to step in clearly has it rattled.

“With the government committed to cut emissions by 81% by 2035 and weather extremes increasing, we can find greener ways to build for urgently needed public transport and flood protection schemes.

“By contrast, trying to green a hugely damaging road scheme is like putting green lipstick on a pig. Not a pretty sight.

“Everyone will end up paying the price if the Lower Thames Crossing goes ahead with private finance.

“It will cause seven years of delays while it is built, for only five years relief at Dartford, with tolls increasing at both crossings to pay back investors.

“It is not fit for purpose and no amount of greenwashing will make it so.”

Mr Todd’s comments came after National Highways outlined its plans to make the project even greener.

It says by working with its partners and supply chain it has managed to halve the predicted construction carbon footprint – and the company has set itself a target of fewer than 840,000 tonnes in total, which is around a 70% cut of the original prediction.

This would be achieved by taking a forensic approach to reducing carbon and committing to only using low-carbon steel and concrete, National Highways explained.

It also aims to remove all diesel from its construction sites by 2027, by accelerating the large-scale use of electric vehicles and plant and using hydrogen to power its heavy construction machinery.

Lower Thames Crossing spokesman Katharina Ferguson said: “The Lower Thames Crossing will not only tackle congestion and unlock economic growth in the UK, with our partners and suppliers we will create a new blueprint for how we build low-carbon infrastructure and leave a legacy of jobs, skills and green spaces for the local community.

“With millions invested in local projects and a new community woodland at Hole Farm on track to open next year, we’re already making a difference, well before work on the new road gets underway.”

The plans to make the Lower Thames Crossing the greenest road ever built in the UK include building a tunnel rather than a bridge to avoid protected wetlands and marshes, and seven green bridges that would provide safe crossing points for people and wildlife.

At least one million additional trees would be planted to create a new community woodland at Hole Farm and new public parks in Thurrock and Gravesham.

National Highways says subject to planning permission and funding, construction is expected to take six years.

The Secretary of State for Transport recently announced the deadline for a decision on the Lower Thames Crossing’s planning application has been extended to May 23, 2025.