The transport secretary has given formal approval to the £9bn Lower Thames Crossing, a road tunnel joining Essex and Kent.

Heidi Alexander granted a development consent order on Tuesday morning, after the decision had been pushed back again last year by the new government.

The controversial scheme has for years been Britain’s biggest single planned road building project, and delays, consultations and redesigns have already cost about £1bn.

The Lower Thames Crossing project will comprise more than 14 miles of roads including the tunnel, which will pass under the River Thames near Thurrock.

The two 2.6-mile tunnels under the Thames will be motorway-sized, with a 70mph speed limit and three lanes in both directions, linking the M25 to Channel port traffic.

The government hopes that private finance will pay for some of the construction, with tolls expected to recoup some of the official £8.95bn “baseline cost” estimate at 2023 prices.

A government source said: “The Lower Thames Crossing will be a key strategic route for drivers, freight, and logistics – improving connectivity between the south and the Midlands, linking up our ports, and unlocking regional economic growth.

“This demonstrates this government’s commitment to delivering the vital infrastructure the country needs to succeed, and to be on the side of the builders, not the blockers.”

More details soon …