Portsmouth needs to spend a staggering £35 million on new defences to combat rising sea levels and storm surges. Hull’s flood defence barrier, which is ageing, would cost £20 million to replace.

London would be ‘ruined’ as a financial centre if it was inundated by a storm surge and Cardiff is in the front line of cities facing the ‘New Orleans’ syndrome.

These worrying factors have been thrown up by boffins at Middlesex University’s Flood Hazard Research Centre as the UK faces exceptional high tides after the full moons of September 7 and October 7. If combined with low pressure and strong south-west winds these high tides could cause serious flooding.