AMK will start work immediately, and a full planning application is expected to be submitted in summer 2014.

The upgrade aims to meet tighter environmental standards, improve the water quality of London’s River Lee and reduce odour.

Lawrence Gosden, Thames Water’s asset director, said: "This is a key moment for us. We believe our Early Contractor Involvement (ECI) process has resulted in the best possible solution for the upgrade, and after close competition between two very high calibre bidders we’re very pleased to announce the appointment of AMK. This project represents the key components of our approach for delivering best value for our customers, working innovatively, sustainably, and in collaboration with our contractors."

Jo Streeten, AMK project director, added: "We’re delighted to be working with Thames Water on this project. Upgrading Deephams presents a number of interesting challenges, not least the need to construct new treatment facilities on a site with limited space, while maintaining the current operation. Working within Thames Water’s ECI process has allowed us to understand these challenges early-on and develop a solution that meets them in the most efficient way. We look forward to working with Thames Water."

The works will be updated to meet strict new Environment Agency sewage treatment standards that will apply from March 2017. The project will also increase capacity to allow for future rises in population, and significantly reduce the frequency and intensity of odour on site.