Freak ocean waves that rise to a height of 10-storey buildings may be sinking ships in accidents that are attributed to nothing more than poor weather.

Once dismissed as a nautical myth, freak or "rogue" waves have been recorded by shipping vessels and more accurately measured from oil and gas platforms at sea.

The waves arise by chance when others combine, leading to giant walls of water that momentarily tower above the rest of the ocean, at heights in excess of 30 metres.

Research at Imperial College, London, shows that far from being rare events, rogue waves can emerge frequently, and may be responsible for some of the 200 supertankers and container ships longer than 200m that have sunk in poor weather conditions in the past two decades.

Chris Swan, who led the study, found that forecasts issued to warn shipping about the risks of rogue waves assume the choppiness of the sea varied little over the duration of a storm.

But he said that a combination of wave tank experiments and theoretical calculations revealed that in small patches of ocean, measuring up to a square kilometre, sea states vary enough to trigger rogue waves.

"We've shown that in a storm, if your ship or platform happens to be in the wrong place at the wrong time, it could experience much more severe wave conditions than you would expect from forecasts, including these freak waves that can cause enormous damage," said Professor Swan, whose study on freak waves appears in the journal, Proceedings of the Royal Society A.

According to Nigel Barltrop, professor of naval architecture at Strathclyde University, so little is known about many shipping accidents, that it can be difficult to know when a rogue wave is to blame.

"A lot of ships, when they go down, there's no real investigation possible without spending a lot of money, so most of them, no one really knows why they sink. These waves aren't like those you see on the beach, they are more like a solid wall of water."

Andrew Linington of the National Union of Marine, Aviation and Shipping Transport Officers, said: "We have to stop calling these freak or rogue waves because all the evidence seems to be suggesting they're to be expected with more frequency than people believed in the past.

"This kind of extreme weather is going to become more common with global warming. There's an urgent need to rewrite the rules of construction for all types of vessels.

"Our feeling is it's too easy to say an accident was a freak wave and right it off as that, but often when a ship falls victim to a wave, it'll be something as stupid as a porthole being broken and water flooding in that causes it to sink. Often, we're talking about bulk carriers and basically nobody cares.

"If these were passenger ships going down there'd be an outcry. There aren't many people in the industry taking it seriously."