More than £1.2 billion has been spent on the Lower Thames Crossing despite construction still not being under way, it has been revealed.

The £9bn project would see a new 14-mile road connect Kent and Essex through a tunnel beneath the River Thames, coming out east of Gravesend, near Shorne, and linking with the A2.

The Financial Times revealed the outlay has risen from £800 million in 2023, with spending on planning, consultations, environmental assessments, traffic modelling, legal fees, land purchases and a new community woodland.

In a briefing document published by National Highways it was also stated that the expected cost of the project will be between £9.2bn and £10.2bn, depending on how the construction phase is financed.

In January, Chancellor Rachel Reeves revealed the government was exploring private investment options for the project.

She said: “We will work with the private sector to deliver the infrastructure that our country desperately needs, this includes the Lower Thames Crossing which will improve connectivity at Dover, Felixstowe and Harwich, alleviating severe congestion as goods destined to export come from the North and the Midlands and across the county to markets overseas.

“To drive growth and deliver value for money for taxpayers we are exploring options to privately finance this important project.”

A proposal to have a “regulated asset base” (RAB) model — in which private investors would collect toll revenues from the road to pay back their investments over the life of the projects — is considered to be favoured by the Treasury, according to people with knowledge of the discussions.

This option would cost the Treasury £200m more in upfront costs than if the government paid for the scheme directly, the National Highways document shows.

The model, which has been used on London’s new Tideway sewer, would require nearly £2bn of taxpayer funding to attract £6.3bn of private investment, taking the total cost of the project to at least £9.4bn, the figures show.

National Highways says there is likely to be a “market interest for the regulated private entity delivery option”, citing projects that use the same structure, including the Sizewell C nuclear plant.

Under the RAB model a new company would be set up by investors to collect revenues from user charges to pay operating and finance costs.

It would also require a new economic regulator to “protect road users and guard against excessive regulated private entity profits”, the documents say.

As it would be the first road to be built under the RAB model, it is likely to require new primary legislation.

The most expensive method of financing the crossing would involve a private finance initiative type scheme, National Highways found.

This would cost taxpayers an additional £1bn, taking the total capital cost to more than £10bn.

Under this option, taxpayers would pay £4.7bn for the tunnel, while a special purpose vehicle set up by investors would draw in £4.3bn in private finance for the roads, with shareholders receiving the toll income over a licence period of 25 to 30 years.

The cost of the tunnel project has already risen from between £5.3bn and £6.8bn when it was first agreed in 2017 to a current forecast of about £10bn.

Chris Todd, director of Transport Action Network, said the project needed a “fundamental rethink” and should be cancelled and replaced by public transport alternatives.

“Smaller, more affordable rail schemes could shift thousands of lorries off our roads and increase connectivity, boosting the economy and social opportunities,” he said.

The government said: “As announced by the chancellor in January, the government and National Highways are exploring options to privately finance the Lower Thames Crossing, and no final decisions have yet been taken. We cannot comment further on this specific scheme.”

National Highways said: “Following a comprehensive programme of consultation and development which began in 2009 and considered a wide range of options, the Lower Thames Crossing remains the best option for tackling the chronic congestion at Dartford and unlocking growth through a new connection between the south-east ports, the Midlands and the North.”

If consent is given this year, construction will start in 2026, ahead of a planned opening in 2032.

A decision on planning consent is expected by May 23, with a ruling on how it will be financed later this year.

Last month, campaigners compared ambitions to make the Lower Thames Crossing the “greenest road ever” in the UK to trying to put green lipstick on a pig.

This followed the announcement of a new target to reduce the multi-billion-pound project’s construction carbon emissions by 70%.