About 12 miles of the flood barriers that protect 1.25 million east Londoners are in a poor state, a new report warns.

A flood could cause damage of up to ₤16 billion in the Thames Gateway area, the London Assembly found after its inquiry into the capital's flood risk.

Flood defences in the recent New Orleans disaster broke in just three places, the scrutiny report says.

About eight per cent of the 139 miles of tidal flood barriers in London are in a "less than satisfactory" state.

Outside the city the condition of two thirds of Thames defences are unknown a fact that is "perhaps more shocking".

If one defence fails, the results could be "catastrophic", the document reads.

In 1953 a tidal surge caused the river to flood, killing 300 people, after which the Thames Barrier was built.

"New Orleans has proved the dangers of complacency when it comes to flood risk," said Darren Johnson, chair of the assembly's environment committee.

"We cannot afford to repeat the same mistakes."

Plans for the Thames Gateway over the next decade include 120,000 new homes and 250,000 more jobs.

Nine out of ten new houses are likely to be in the floodplain, most of which is protected.

The region is already home to 1.25 million people - more than the population of Birmingham. It has half a million properties, including eight power stations, 400 schools and 16 hospitals.

Yet a "patchwork quilt" of at least 14 bodies shares the job of preventing floods.

It is often unclear who has to repair what barrier, or which rules apply to plans for new buildings.

This puts London at risk, the report warns.

The assembly's environment committee approved the report yesterday after its eight-month inquiry.

It called for a survey of all flood defences in the Thames Estuary, as well as better coordination of policy in the area.