It measured F5 on the Fujita scale, which means it was the most severe. And so Greensburg, Kansas, is the latest US state to find itself devastated by the biggest terrorist currently stalking America: the killer tornado. We're bang in the middle of the season, which started in February and will last until July. According to official statistics, tornados kill an average of 70 Americans each year.

The Greensburg tornado, which touched down on Friday, was a mile wide, tore through the town at a terrifying 165mph, destroyed 95% of the town and killed 10 people.

It's just the latest in a series of terrifying twisters that since February this year have been terrorising the southern states of Georgia, Alabama and Florida.

Tornados - violently rotating columns of air - develop at this time of year because cold, dry air moving south and east from across the Rockies meets warm, moist air from the Gulf of Mexico. The part of the US with the highest number of tornados per square mile is central Oklahoma.

Many nervous onlookers are beginning to suspect climate change is heightening not only the frequency and intensity of tornados, but also the likelihood of their hitting Britain. So is it time to batten down the hatches?

No, says Torro, the British tornado and storm research organisation. "Thankfully this kind of tornado is very rare," says spokeswoman Samantha Hall. "Most tornados are F1s, the kind that are described as ropey' and don't do much damage."

But Birmingham had one in 2004 and again in 2005, and London was hit in December 2006. They made headline news due not to the damage they caused (they didn't), but to their gasp factor. And although Torro says they are most rare in Northern Ireland and Scotland, we did have a mini one in Lanarkshire as recently as August last year.

The small twister, reported The Herald, was spotted on the evening of August 17 and the Met Office said it had the power to cause structural damage. It brought thunderstorms to East Kilbride and was also spotted in Drumclog, but in the end no damage was done.

Even so, we shouldn't panic. "There's no evidence to suggest an increase in frequency," asserts Hall. "Most tornados in the UK are very localised and don't cause damage."

The reason it seems unusual for us to get tornadoes is because we're such a small country. Our weather passes quickly, so a storm doesn't get the chance to develop and create the deadly supercell (violent thunderstorm) and circular rotating updraft the way it does in the wide US land mass. Thanks to the UK's relatively small land mass, by the time a storm has been created it has usually gone to sea.

However, the UK actually has the highest frequency of reported tornados in the world - once you take land areas into account. Obviously a large nation will report many tornados simply because of its large area, but when you do the sums, like the American meteorologist Dr T Fujita did in 1973, Britain actually experiences more. It turns out that on average, 33 tornados are reported each year in the UK. This average is based on a 30-year period, though the actual yearly figures may vary dramatically from year to year.

Most reports come from the West Midlands, East Midlands, central-southern England, south-eastern England and East Anglia. Some occur in south-western England, north-western England, north-eastern England and Wales.

Hall claims there is no evidence that the effects of climate change will bring more. "We don't know what climate change will have in store for us, but there's nothing to suggest that will happen," she says.

However, that's not what Dr David Viner of the Climatic Research Unit at the University of East Anglia said earlier this year, when commenting on the reasons Birmingham has suffered two tornados in recent years.

The acclaimed scientist, who contributed to the recent inter- governmental panel on climate change, reckons freak weather, such as tornadoes, will become increasingly common due to the "urban heat island effect".

He told the Birmingham Post: "Hot summer temperatures, coupled with air pollution and the tendency for extreme storms, will make Birmingham an unpleasant place to live."

But Torro doesn't agree that anybody can predict the effects of climate change with any certainty.

"Torro looks at statistics which are collated each time a tornado occurs, and while our severe weather machinery is very good, it can't forecast beyond five days. So how anyone can suggest what's going to happen because of climate change is beyond us," says Hall.

So, another reason to be cheerful that we live in a small country? Or a warning to keep a watchful eye on the weather forecast? You decide.