Global warming is not a distant threat - it is happening now and in the UK, according to a report.

And whatever we do to reduce our impact on the climate, it is inevitable that sea levels will continue to rise for at least the next five centuries, warns the World Wide Fund for Nature-UK.

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WWF says the Hadley Centre for Climate Research, part of the Meteorological Office, has calculated that sea level rise is irreversible before 2500 for one reason.

"The problem is the oceans", says the report. "So far, only surface waters have warmed up as a result of the higher temperature of the atmosphere".

"The long process of warming the middle and lower depths has barely begun."

WWF says that up to half of the world's coastal wetlands may be lost over the next century. Low-lying countries like Bangladesh and Egypt, many with huge populations, face the greatest threat.

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And with scierntists predicting an average sea level rise of between 38 and 55cm by 2100, some small island states could disappear beneath the waves.

The Foreign Minister of the Marshall Islands, in the Pacific, says rising sea levels could annihilate his country "as effectively as an atomic bomb".

WWF says sea level rise is a reality for parts of the UK today. It says many miles of the East Coast of England are at risk.

The problem is made worse by the fact that south-east England is actually sinking slightly every year.

In the next 20 years, the report says, Britain is likely to lose at least 13,000 hectares (130 square kilometres) of saltmarsh, mudflats and coastal lagoons.

These are areas vital for wildlife. They are also home to thousands of people.

And some of the threatened coastal land is already used by industry.

The sea wall on the southern side of the Humber estuary protects two power stations, a steel works, an oil store and a port.

Yet the wall is already being eaten away by the scouring of the tides.

Dr Ute Collier of WWF says other coastal installations could be at risk, including Sizewell nuclear power station in Suffolk.

"That is probably safe for the next 20 years", she says. "But in 50 years it could be under threat".

'Surrender'

WWF says part of the answer is "managed retreat". This means surrendering to the sea the parts of the land it would be too difficult or expensive to protect.

The difficulty with that approach is persuading people that moving out is the only thing to do.

John Gummer, Conservative MP for the Suffolk Coastal constituency, with 74 miles of shoreline, says the UK is not taking the issue seriously.

The former environment secretary adds that most of us are "pulling the bedclothes over our heads".

The Ministry of Agriculture has also cut sea defence spending, he said.