Construction of a controversial road tunnel in east London will start next year after Transport for London (TfL) signed the contracts today.

Silvertown Tunnel will link Greenwich and Newham near the existing Blackwall Tunnel. It will cost £1 billion and is due to open in 2025.

The crossing will be tolled, and a user charge will also be introduced on Blackwall tunnel.

Although it was not in his 2016 manifesto, Sadiq Khan has championed the Silvertown project.

With major developments ongoing on both sides of the river, he believes the tunnel will reduce traffic congestion and improve air quality for residents.

But campaigners and opposition politicians say a new road will encourage more traffic, and worsen air pollution in some areas.

Lewisham, Greenwich, Newham and Hackney councils have all called on the Mayor to reconsider his plans, with Tower Hamlets the only nearby borough still backing the tunnel.

Silvertown will be within the expanded ultra-low emission zone, and TfL has pledged to increase bus services from six to 37 an hour at peak times, and to invest in walking and cycling routes.

But though the transport authority claims air quality will improve, its own analysis suggests that toxic air pollution will go over legal limits at some sites near the tunnel.

Victoria Rance, Green party parliamentary candidate for Greenwich and Woolwich and spokesperson for Stop the Silvertown Tunnel Coalition (SSTC), said the Mayor had “betrayed Londoners” with today’s decision.

She said: “Silvertown Tunnel is a four lane motorway with HGV lanes, which will worsen air quality for hundreds of thousands of residents throughout east and south east London, where air pollution is already over legal limits.

“Mayor Khan has ignored advice from climate, environmental health and traffic experts and is pursuing the Silvertown Tunnel without any democratic mandate.

She added: “He has decided to inflict this new road on the citizens of London – the vast majority of whom don’t want it – despite opposition from neighbouring councils.”

SSTC believes the Mayor should consider a high toll on Blackwall tunnel to ease congestion without a new road.

And Ms Rance confirmed that the group will launch a judicial review of TfL’s decision – likely on that basis.

Green London Assembly member Caroline Russell, who chairs the Assembly’s environment committee, described today’s decision as “the worst the Mayor could have made”.

She said: “Sadiq Khan is locking the next Mayor of London into building a climate-busting road tunnel, and he’s locking south east London into years of heavy traffic.”

Highlighting the penalty costs of cancelling projects once contracts have been signed, she said: “We know from the Garden Bridge what happens when you unravel contracts. He’s potentially wasting a lot of public money here.”

Ms Russell said it was “extraordinary” that Mr Khan calls himself a green Mayor in light of plans the plans for Silvertown Tunnel.

She said: “People are worried about increased traffic, air pollution, road danger, and community severance.

“The Mayor is obviously trying to bury bad news. This has come right in the middle of an election campaign and on the back of the Uber decision today.

“If the ink isn’t dry yet he should rip the contract up.”

Liberal Democrat Caroline Pidgeon, a former chair of the Assembly’s transport committee, said the decision showed the Mayor “has the wrong priorities”.

She said: “If Sadiq Khan was truly confident of the arguments for Silvertown Tunnel he would put it in his manifesto for next year’s Mayoral and London Assembly elections. Why is he so afraid to do this?”

A spokesperson for the Mayor said Mr Khan welcomed the sign off on the tunnel “which will enable us to progress our essential plans for more river crossings in East London”.

He said: “A new tunnel at Silvertown – combined with the introduction of tolls on both the Blackwall tunnel and at Silvertown – will play a crucial role in tackling congestion, improving air quality and providing much-needed additional bus services across the river.”

A TfL spokesperson said: “The Silvertown Tunnel has been designed to reduce congestion around the Blackwall Tunnel, as well as enable new cross-river bus routes to be introduced.

“The traffic modelling demonstrates that overall traffic does not increase as a result of the Silvertown Tunnel scheme.

“This is because the user charge can be set to manage demand for the Silvertown and Blackwall tunnels.”