The extension of the main tunnel section under the Thames connecting Kent, Essex and Thurrock is one of several design changes to access roads, tunnel entrances and junctions on the route.

Despite these alterations following initial public consultations officials say the project is still within its £5.3bn and £6.8bn projected budget.

But plans to submit a development consent order in 2019 have slipped back by over six months as a result with a new submission now expected to be submitted in summer 2020 after a fresh wave of final consultations.

The project involves constructing the world’s third-widest bored tunnel. The southern tunnel entrance in Gravesend has been moved 350m further south to reduce impact on protected bird habitats in the Ramsar Marshes and the Thames Estuary.

Project involves driving two 2.6-mile (4.3km) tunnels beneath the Thames

It is likely to take around six years to build the tunnel and the road within the tunnel.

Chris Taylor, Director of Highways England’s Complex Infrastructure Programme, said: “The Lower Thames Crossing is Highways England’s most ambitious project in 30 years, designed to improve journeys across the southeast and open up new connections and opportunities for people and businesses.

“Once the consultation closes in March, Highways England will analyse the new responses ahead of finalising its plans to seek planning consent for the project, through submitting a development consent order.”