Thames Tideway, the company building London’s £4.3 billion ‘super sewer’ under the Thames is to launch a bond sale to raise £200-£400 million extra financing for the 25-kilometre tunnel.

The company met with 15 investors to secure financing for the project until at least 2020. The remainder is to be raised before construction is completed in 2024. The project is intended to reduce the tens of millions of tonnes of sewage that overflow into the waterway every year.

“We have a supportive group of shareholders, attractive financing and a first class group of delivery partners, so all the building blocks are in place to start work on this landmark project for London,” said Andy Mitchell, chief executive of Tideway.

Almost one billion pounds of construction contracts have already been awarded to lead contractors including Costain, the engineering group, for the eastern section of the river, Balfour Beatty, in the South-West, and Ferrovial Agroman UK for the central section that will be built under the parliament buildings.