Britain's biggest engineering businesses are circling a project designed to protect 1.25 million Londoners and £200bn of property from flooding until the end of the century.
The Environment Agency will ask for bids for the first phase of the plan, which will ultimately include a revamp of the Thames Barrier, in September. Atkins, Arup, Halcrow, and Hyder Consulting are all thought to be preparing bids to run the first 10 years of what is known as Thames Estuary 2100. The first quarter-century of the scheme is valued at £1.4bn.
This includes work to replace and improve tidal flood defences as water levels in the Thames Estuary are likely to rise between 20cm and 90cm over the next century, as climate changes melt glaciers and ice sheets. For example, Kingston in the South-west of the capital could see peak flow increase 40 per cent by 2080.
Built after the 1953 floods which killed around 300 people and destroyed 24,000 houses, the Thames Estuary flood defences' natural lives will come to an end during the next 50 years.
The Thames Barrier itself was built to withstand the type of severe floods that could occur only once in a millennium. However, the Met Office recently found that there is likely to be a greater frequency of torrential rain in the coming decades, particularly during the winter.
An industry source said: "This is a huge project, with all the flood defences and design work needed.
"For an engineer working in this type of sector this is one of the most important bids to work on – a key contract."
A replacement for the Thames Barrier could be built between 2050 and 2070. An Environment Agency report published in November said: "Thames Estuary 2100 is the first major flood risk project in the UK to have put climate change adaptation at its core.
"Hard choices need to be taken – we must either invest more in sustainable approaches to flood and coastal management or learn to live with increased flooding."
An Environment Agency spokesman confirmed that the bidding process will start in the autumn.