British cities near the coast are at risk of extreme flooding with urgent action needed now to protect them, the RIBA and the Institution of Civil Engineers have claimed.

A new report by the two organisations urges the government, built environment professionals, planning authorities and the public to focus on devising radical solutions including the building of flood defenses or floating or stilted buildings.

The report, called Facing up to Rising Sea Levels: Retreat, Defend, Attack?, focuses on Kingston upon Hull and Portsmouth and presents six scenarios up to 90 years in the future, proposing three main approaches to tacking extreme flooding – retreat, defend or attack.

RIBA president Ruth Reed said: “The scenarios we have created are extreme, but it is an extreme threat we are facing. Approximately 10 million people live in flood risk areas in England and Wales, with 2.6 million properties directly at risk of flooding from rivers or the sea.

"However, if we act now, we can adapt in such a way that will prevent mass disruption and allow coastal communities to continue to prosper. But the key word is now.”

Chairman of the ICE steering group Ben Hamer added: “A proactive and united, almost war-like approach is needed if we are to win the battle against what is set to be our biggest challenge in the next century, the ‘water invasion’.”

The project, including sketches and details of the proposed ‘new cities’, will be exhibited at the Building Centre, London 6th Jan – 29th Jan 2010, before travelling to Portsmouth 15 - 27 February, and Kingston-upon-Hull 15 – 28 April 2010.