The European Investment Bank (EIB) is to provide a £700m loan for the £4.2bn Thames Tideway Tunnel.

The ‘super sewer’ will help tackle overflows of untreated sewage into the river. The backing for the project represents EIB’s largest-ever loan for water investment worldwide.

The 35-year long-term loan has been agreed with Tideway, the new regulated company set up to design, build, commission and maintain the 25km tunnel, which will directly control or intercept discharges from more than 30 combined sewer overflow points, from Acton in the west to Stratford in the east.

“The new £700m loan for Tideway represents the European Investment Bank’s largest-ever water loan and the most significant support for UK infrastructure since Crossrail,” said EIB vice president Jonathan Taylor. “This demonstrates the EIB’s strong commitment as the largest source of financing for long-term investment in UK water infrastructure since before privatisation and builds on more than £2bn of support for investment to improve London’s water and waste water infrastructure since 1989.”

Tideway chief financial officer Mark Corben said: “The EIB’s backing for Tideway is an important vote of confidence in us as a company, as we move into the construction phase. This loan covers a significant proportion of the financing we need to raise.”