More than one million extra trees will be planted as part of the Lower Thames Crossing project.

A community woodland and two public parks are among the 400 hectares (1,000 acres) of "landscape-scale" forest creation planned as part of the proposals.

Plans include planting the trees across Kent and in Thurrock, Havering and Brentwood in Essex to help the 14-mile multi-billion pound project address its impact on the environment.

National Highways hopes the crossing will be the greenest road ever built in the UK but campaigners at the Woodland Trust have criticised its impact on “irreplaceable” ancient woodland, wildlife and increased carbon emissions.

Laura Blake, Chair of the Thames Crossing Action Group added: “You cannot talk about caring for the natural environment whilst proposing such a hugely destructive and harmful road project.

"Much of the land where they are proposing to plant these trees is agricultural land that they want to take for compensation for the harmful nitrogen pollution the project would cause.

"It also increases the thousands of acres of farmland that would be lost if the it goes ahead, at a time of major food security concerns."

The project aims to almost double road capacity across the Thames east of London and ease congestion on the Dartford Crossing.

It is said the new route would connect residents to jobs, boost the economy and create new public parks and woodland habitat.

Matt Palmer, executive director for the Lower Thames Crossing, said: “The Lower Thames Crossing will tackle the daily frustration caused by the congestion at Dartford, improve journeys and bring exciting opportunities for new jobs and businesses across the region, but we are determined that this will not come at the expense of the environment.

“We have planned its route and how we build it to not only reduce its impact but leave a legacy of bigger, better-connected and well-managed habitats that would give local wildlife and plant life the chance to thrive long into the future.”

The “landscape scale” proposals would include public parks in Thurrock and Gravesham, a new community woodland in Brentwood, and other areas of native broadleaf trees and habitat creation, including grassland, hedgerows and ponds, from Maidstone in Kent to Upminster in the London Borough Havering.

The area of ancient woodland lost by construction of the new road has been reduced to less than 12 hectares, National Highways said.

While the roads agency acknowledges that the ancient woodland is irreplaceable, it says its strategy will provide six times as much woodland as that lost.

Laura Blake continued: "This is not mitigation, when you minimise the impacts, this is compensation, when you acknowledge the damage that has been done, because they can’t find a way to minimise or stop the pollution.

"A huge chunk of this proposed compensation land is at Hole Farm, near Great Warley, which National Highways have already publicly stated is part of their national plans to ‘improve’ biodiversity along their major routes, in this instance the M25.

"Since they have stated these plans are going ahead regardless of whether the LTC gets permission, they should not be counted as part of the LTC project, It is creative accounting and yet more greenwash nonsense.”

Jack Taylor, lead campaigner, Woodland Trust, said: “No number of new trees compensates for the loss of irreplaceable ancient woodland; centuries old and nature’s own carbon stores.”

He also criticised National Highways for saying it could transfer soil from cleared ancient woodland as part of efforts to create new habitat as “touting a flawed concept”.

“They are quick to talk about what they’ll plant and create, but very resistant to disclose what will be destroyed in the first place.

“We’re fighting both a nature and climate crisis, and destruction like this for a road scheme beggars belief,” he said.

The most recent consultation into revised plans ended last Monday.

An application for a Development Consent Order will be submitted later this year.