A bid to build Britain's longest road tunnel to ease congestion on the Dartford Crossing has been accepted for review despite being labelled "low value for money".

The revised application to build the Lower Thames Crossing connecting Kent and Essex via a new 14.3 mile road was resubmitted last month.

It includes two 2.6-mile road tunnels under the Thames, which will be the longest road tunnels in England.

The project requires changes to the current road network and requires approval from the government in the form of a development consent order (DCO).

Earlier today it was confirmed a DCO application for the new crossing was accepted for review by the Planning Inspectorate which allows it to proceed to the next stage of the planning process.

National Highways says it will double road capacity across the Thames east of London and reduce congestion at the Dartford Crossing.

But the project has come under fire over its eco-credentials and whether it provides taxpayers with value for money.

An initial bid was pulled at the 11th hour in November 2020 after it emerged the Planning Inspectorate was poised to reject it over environmental concerns and a lack of detail ahead of the review stage.

Since then the cost of delivering the project has continued to climb and the start date has been set back to 2024.

The National Audit Office now estimates the project will cost up to £9bn to deliver – an increase of nearly £2bn since March 2020.

In its latest report assessing the financial health of major government infrastructure projects, the public spending watchdog said costs have increased due to delays and inflationary pressures.

It adds delays to the DCO submission and the "broadened scope" of changes needed to meet safety and environmental requirements had also been factors.

Delays have in part been caused by the requirement to re-design the project following the introduction of government’s policy on freeports due to an overlap between land required for the proposed Thames Freeport and Lower Thames Crossing project.

According to the public spending watchdog, the project has the largest forecast underspend of any project due to the hold-up.

It means that, by March 2025, National Highways will have undertaken less work on road enhancements and at a higher cost than originally planned.

The government-owned transport company tasked with delivering the tunnel link is forecasting it will have spent £1.5 billion less than planned by that time.

As a result construction activity due to take place has now been moved to the next road period and will require funding.

The £9bn road scheme also features on a government watchlist – alongside the controversial Stonehenge Tunnel project – rated by auditors as "low value for money".

Compared to its northern neighbours spend on large transport and infrastructures projects in the South East has increased by £393 per person, largely driven by cost increases on the Lower Thames Crossing project.

"This review must consider if these projects remain feasible and provide optimal value for money.”

Gareth Davies, the head of the NAO said it had been "unfortunate" the bid had coincided with the pandemic and rising inflations.

But added: "Nevertheless, more could have been done to manage risks. Delays to projects have meant that less work has been delivered than planned and at a higher cost.

"The Department for Transport and National Highways must now fully address the rising cost of its revised portfolio of projects, undertaking a review of all road plans that it plans to move into the time-period of its third road strategy (2025-2030).

"This review must consider if these projects remain feasible and provide optimal value for money.”

If approved by the Secretary of State, the NAO also warns the project will likely face opposition from environmental campaign groups.

Planners for the 2.6 mile tunnel link previously revealed a target to plant 1 million trees following criticism that farmland could be used to soak up fumes generated by the scheme.

National Highways say there’s also been a reduction in the number of properties that would be directly impacted by construction.

However, the results of a recent survey show there remain strong objections to various aspects of the scheme.

Thurrock Council has also come out in opposition to the project amid "significant concerns" about the impact of the new crossing on local roads and its "smart motorway" credentials.

But its supporters – including Dartford council and Dartford MP Gareth Johnson – say "there is no alternative" and it must go-ahead without any further delay.

Nick Harris, National Highways’ chief executive, said “external factors” have had a “significant impact" on its ability to deliver a complex programme but progress is being made.

He added: “Despite these challenges, we have successfully received consent to deliver several major infrastructure developments.

“We’re confident that we manage portfolio and project risks well, while recognising that there is always room for improvement as we mature our processes ready for the third road investment strategy RIS3.”

The planning process is likely to take around 18 months including six months of examination, some taking place at public hearings.

National Highways says when built the Lower Thames Crossing will be the "greenest road ever" in the UK.

A tunnel was chosen rather than a bridge to avoid protected wetlands and marshes, seven green bridges would provide safer crossing points for people and wildlife, and viaducts are planned to protect a nearby flood plain.

Matt Palmer, executive director for the Lower Thames Crossing said: “The Planning Inspectorate has accepted that our comprehensive programme of consultation and design development has been undertaken properly, meaning our plans can now be taken forward for robust and thorough examination by independent, government-appointed experts."