The iconic Thames Barrier has marked four decades of protecting London from the perils of flooding, but may become obsolete by the end of the century, climate experts are warning.

The barrier was officially opened by Queen Elizabeth on May 8, 1984, after almost a decade under construction and stretches across the river from Silvertown to Woolwich.

It is one of the largest movable flood defence barriers in the world, saving the metropolis from rising tides and seasonal estuary surges from the North Sea.

But climate change in the past 40 years has led to more extreme weather, especially for low-lying areas like London. Rising sea levels and rapid urban growth add to the complexity and need fresh solutions, the Institution of Civil Engineers suggests.

Industry experts and barrier engineers are being invited to join the institution on May 9 to look into future flood defence needs.

The barrier is on the frontline of flood defence — but cannot stand alone, the organisation warns.

A ‘Thames Estuary 2100’ plan is looking at defence strategy for the next 75 years and identifies three thresholds that need action — from current defences becoming inadequate to a scenario where even an improved barrier “may not be enough to hold back the floods”, the Environment Agency has revealed.

“The ‘Thames 2100’ plan is our determination to fortify London’s defences,” Thames Barrier manager Andy Batchelor said.

“The barrier has provided protection for the past four decades and will continue for many years to come.

“But our plan ensures we take the steps needed between now and the end of the century to bolster London’s resilience to climate change, free from worries about the threat of flooding.”

Mr Batchelor’s first day managing the barrier was when it was officially opened in 1984. He is stepping down on its 40th anniversary, but is continuing as chair of I-Storm, the international network of storm surge barriers that he co-founded in 2006 with specialists around the world.

Construction of the Thames Barrier began in 1974 and was completed by 1982. It was first used in earnest in 1983, but was not officially opened until May 1984. It has been closed 221 times since, including 119 times against tidal flooding.

The earliest recorded flood in London was in the Anglo Saxon Chronicle in 1099. The last time London was severely flooded was in 1928, when 14 people were drowned.

A huge tidal surge in the Thames estuary in 1953 caused 300ft of sea wall to collapse, flooding Canvey Island.

Areas predicted to be affected by flooding by 2050 include a large swathe of east London from Poplar and the Isle of Dogs to Plaistow, Ilford, Dagenham and Romford, while on the south side areas in danger could include Rotherhithe, Greenwich, Woolwich, Thamesmead and Dartford.