The plan comes as part of a wider range of spending curtailing by the incumbent Labour government as it seeks to increase private investment in public transport, infrastructure and public utilities.

The proposed investment plans could be closer to projects such as Thames Tideway, the new London sewer utilising a regulated asset-based model.

Unlike traditional PFI contracts, where investors received guaranteed payments from taxpayers, London residents are paying for the Tideway through additional user charges in water bills.

The Lower Thames Crossing has been planned for more than 10 years to create a relief road under the river for the M25, running east of the Dartford Crossing. The A122 Lower Thames Crossing would connect to the A2 and M2 in Kent to the A13 in Thurrock and junction 29 of the M25 in the London Borough of Havering.

It would be approximately 14.3 miles long, with 2.6 miles of this in two tunnels under the Thames – making them the longest road tunnels in the UK. The tunnels would be located to the east of the village of Chalk on the south side of the Thames, and to the west of East Tilbury on the north side.

When built, the crossing will have a free-flow charging system, similar to that of the nearby Dartford Crossing. According to official documents, roughly £800m has been spent on the framework for the Lower Thames Crossing already.