Lobbyists are urging Boris Johnson to back the controversial 17-mile Thames sewer tunnel planned to be built under the riverbed.

The Mayor of London is being asked to endorse Thames Water’s submission to the Government’s Planning Inspectorate next Thursday for the tunnel to run from Barnes to the Isle of Dogs.

The ‘Thames Tunnel Now’ pressure group want the project to go ahead to tackle the river sewage pollution they say has got worse during 10 years of debate.

“We cannot afford to delay this desperately-needed action any further,” said Thames21 environment charity’s Debbie Leach. “Raw sewage is still entering the river at least once a week, threatening fish, birds and mammals that depend on it, as well as human health.”

The Mayor was an early supporter of the project, the pressure group points out, so it wants him to “stand his ground” and not be swayed by opponents.

Boris was lobbied heavily last year by opponents right along the river, including campaigners fighting to save Shadwell’s King Edward Memorial Park where Thames Water wants to put up a towering sewer ventilation shaft on the foreshore.

He joined Tower Hamlets Council in promising support for the Shadwell campaigners.

But now the ‘pro-Tunnel’ lobby wants him to revert to his original stand.

River Thames Society Chairman Peter Finch said: “Our sewerage system urgently needs more capacity to meet today’s needs.”

London’s sewerage network was created by the leading Victorian civil engineer of his day, Sir Joseph Bazalgette, to tackle the cholera epidemic of the 1860s.

But the population was only two million back then. The ageing, overworked network is now handling sewage for a population five times that, with frequent overflows into the Thames, the pro-lobbyists point out.