The scheme, including a flood relief channel along the River Thames, could go unfunded by the government, the Thames Flood Forum (TFF) has said.

The Environment Agency said there were 30,000 people at flood risk in the area between Datchet and Teddington.

But it said the flood risk area was considered low priority by Defra.

Flooding in the Datchet area has previously cost millions of pounds.

Residents claimed a flood relief channel, the Jubilee River, built to alleviate floods in Maidenhead, has exacerbated any flooding problem downstream.

Tom Crossett, TFF chairman, said: "We believe it is unlikely to be funded by the government in the foreseeable future.

"We believe it is outrageous that the largest undefended flood zone in England and Wales, containing nearly 30,000 people, should remain under threat with residents finding it ever more difficult to insure homes and businesses."

The Environment Agency's Lower Thames Strategy said the cost of a flood relief scheme which would include a flood relief channel, similar to the Jubilee River scheme, would be £200 million.

£259 per head

It has said this flood plain holds the largest number of properties and people in a single location at risk from river flooding in England and Wales.

Mr Crossett has said the community paying for the scheme could be a viable option.

"£200 million sounds like a lot of money, but does £259 per head per year for 10 years sound better?

"Boscastle [flooding in 2004] was a one in 400 years event, the Lewes flood [2000] was very rare, but there's no reason why it couldn't happen tomorrow."

The Environment Agency have said the Lower Thames Strategy has a low Defra priority score and would be reviewed again in 2010.

Number of projects

In a statement, a spokesman, for Defra, said no submission for the Lower Thames Strategy has been received so it was not in a position to comment on the detail.

"Defra is currently funding a large number of projects around England, both inland and coastal, and will continue to do so.