Purpose-built islands designed to break up potentially devastating tidal surges in the Thames estuary could double as airport runways, according to a report.

The suggestion has been floated by the Thames Estuary Steering Group investigating possible options for an off-shore
island off north Kent.

The group is an expert panel appointed by London Mayor Boris Johnson to examine the potential for development around the river - including the highly contentious option of building a £40bn airport.

In a 50-page report, the group - which includes the renowned architect Sir Terry Farrell - puts forward the idea of using high-tech flood defences in the form of man-made islands as runways.

And it says an off-shore scheme - dubbed Boris Island - should be considered because of the problems of extending existing airports and developing regional ones.

The report states: "An earlier argument saw that islands in the estuary can be part of flood defences.

"Such islands could also be put to dual use as runways.

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"Further thought on the availability of airspace and its control across the channel then also becomes relevant – an analysis which is also necessary for an expanded use of Manston or Southend."

The report makes clear the group believes that of all the options for expanding aviation capacity, the estuary scheme has most advantages.

It said: "Balancing benefits and disbenefits of alternative locations for expansion is tricky.

"All locations would impose costs of local communities - minimising these gives weight to an offshore location."

Bridget Rosewell, a leading member of the group and a former adviser to the mayor, said the airport idea warranted further investigation - despite the wide-ranging opposition and the fact that it has all but been ruled out by David Cameron.

She said: "What we are saying is that this could be a possibility and merits further investigation.

"We are certainly not saying the airport plan is a no-go option but that more work needs to be done."

The renewed backing for the airport scheme will dismay long-standing opponents across Kent and Medway.

"Late last year, the Prime Minister signalled that the government had no intention of supporting the proposal as part of its aviation policy.

Sheppey MP Gordon Henderson was dismissive. "They are going to keep going on about this right up to the London mayoral elections. It is just a sop to keep the electors of London happy.

"David Cameron has made it perfectly clear thta he ‘s not going to support it."

Read the report "The Thames Estuary: An Integrated Approach" here:http://bit.ly/hB2DB5