It lasted less than a couple of minutes. First, the skies suddenly blackened over London, then there was a flash of lightning and thunder, followed by a maelstrom of rain and hail.
But then came the terrible wind, rapidly forming itself into a twister that tore its way through a cluster of suburban roads with the force of an express train, then dissipated as quickly as it had arrived.
In just a few seconds, the tornado that ripped through Chamberlayne Road and adjoining streets in Kensal Green in north-west London at 11.02am yesterday caused millions of pounds of damage, tearing off roofs and uprooting trees, turning over cars and flattening fences.
Residents described a "huge wind" that shook walls like a passing train, and "sucked up" roof tiles, trees and garden furniture, depositing them in a rain of debris that littered the streets. More than 100 houses were damaged in only about a quarter of a square mile - some so severely they are likely to be demolished - and about 100 people were left homeless for the night. Bertha Joseph, the Mayor of Brent, said: "It was like a horror movie.''
Amid the scale of the damage and chaos, it was remarkable that only one person was seriously injured and had to be treated briefly in hospital; five others suffered minor injuries and shock. Most of the injuries were as a result of being hit on the head by flying objects.
The tornado was part of a wave of bad weather across the country which caused flooding, affected roads and rail services and led to the cancellation of flights out of Heathrow. A series of such freak storms have hit Britain in the past few weeks, although meteorologists are reluctant to draw any link to global warming, saying the increased frequency may simply be due to more observant people.
Last week, tornadoes were reported in west Wales and Hampshire and in September, Leeds and Lincolnshire were hit, all with varying degrees of destructiveness. The most serious incidents in recent years came in July last year when parts of inner-city Birmingham were struck by a severe tornado which caused massive damage.
Yesterday in Kensal Green, Miko Adams, a travel agent who lives with his family on Chamberlayne Road, said: "I was in the bedroom when suddenly there was this thunder and lightning. I quite like a bit of a storm, so I went to the window to have a look and there was this sleet and hail. Then the wind picked up very fast and hard. I grabbed the window to stop it rattling and it felt like the wall was being pulled out; I thought the chimney was coming down. Then it was all over in about 15 seconds, it was amazingly quick.
"We were lucky, unlike our neighbour, who had most of her roof pulled off. There's a tree in our garden from the neighbours, the fence has fallen down and we've probably lost a few roof tiles. And the garage roof, which is corrugated iron, has disappeared completely." His wife and baby, who were out, have been unable to return and had been forced to stay with friends.
In Oakhampton Road, Donna Gay's roof was ripped off, landing in the yard of the neighbouring primary school. She said: "I heard what sounded like a thunderstorm just outside and it felt like the window was going to crash in. All of a sudden the whole roof lifted off into the school next door. I didn't realise at first until I saw all the people coming out of the shop and pointing. It was a good thing the children were not out playing because otherwise we could have had some deaths." The school was evacuated.
Maya Sendall, an actor, who lives on Chamberlayne Road, said: "It was just like a train going past. The house shook and I thought the wall was going to come off the building. The sound of the wind was astonishing." Another resident. Colin Brewer, said: "It was really, really incredible. All of a sudden I saw a swirl starting to form and then, it was amazing, but it then touched land. I then saw clumps of all sorts of things flying into air. It went from exciting to terrifying."
Tim Klotz, said he saw the tornado from his house. "It was like some sort of cyclone. I was actually in an attic room working at my desk on the computer and there was heavy rain and sleet and then the wind just really changed. I looked up through a skylight and debris was falling through the air. I heard what seemed like large, clay dominoes falling, which I think were roof tiles."
An emergency operation was launched by police, the emergency services and Brent Council, which was still continuing last night. Many residents returned home from work yesterday evening to discover they were unable to reach their homes, which were still cordoned off as structural engineers and fire officers made safety and structural checks. Many roofs still had large numbers of loose tiles at the mercy of gusting winds, and objects remained lodged in trees. Dave Bonner, a general manager for the London Fire Brigade, said: "We cannot let people back into the area while the conditions remain dangerous."
Fire officers were setting up powerful arc lights so that the work could continue throughout the night. The commuters were forced to join up to 100 other residents in a church hall but all later moved to a community centre in Kilburn. One resident said she had not been able to see the extent of the damage and was not expecting to be able to return until this morning. Murline Morrison said: "The roof has been damaged and the windows have been blown in. I've got nothing, only what I'm wearing."
Andy Hardy, the borough surveyor for Brent, said some properties were uninhabitable and the council was preparing to rehouse the people affected. He added: "There are a number of houses which may have to be shored up or demolished. We are expecting further severe weather so we are not going to send any contractors in to shore up until we are sure the weather is not going to create further mayhem."
The damage to buildings and cars is expected to be covered by insurance policies, said the Association of British Insurers. Last year's Birmingham tornado cost "tens of millions" of pounds. Weather experts said yesterday's tornado started in a line of thunderstorms that spread from Cornwall. Atmospheric conditions caused it to gather speed as it neared London, and a change in wind direction ahead of it may have caused the rotation.
The storms affected west coast main line services after a Glasgow to London train became stuck in Buckinghamshire because of an overhead wire problem. The weather also caused signalling problems which delayed trains from London to Cardiff. Sixty flights from Heathrow were cancelled.
Assurances that the tornado was unconnected to climate change were greeted with scepticism by some. Dawn Butler, the Labour MP for Brent South, said: "This is a sign we have to take it seriously and we have to look at how we live. It is devastating."
Frank Hewetson, a Greenpeace official, who was buffeted by the tornado near his home, said: "I was lucky not to be hit. There are so many examples of strange weather events now that we can't write it off. Some people will say it's not climate change, but I don't think we've had too many twisters in Kensal Rise."
How winds get in a spin and become a destructive force of nature
Tornadoes are violently rotating columns of air that usually form in the unstable atmosphere of a thunderstorm, when winds of opposite directions meet and start a column of air spinning.
Put crudely, the process is rather like rolling a cigarette. Fingers push one way round the cylinder of paper and tobacco, thumbs push the other, and it revolves.
Tornado formation is this process, scaled up millions of times to produce extremely high wind speeds which can pose a real threat to property and life on the ground (in the most extreme cases they can hit hundreds of miles an hour).
The most propitious conditions for tornado formation are when a mass of warm air from one direction meets a mass of cold air coming from another, and this is what happens in the world's most tornado-prone area, "Tornado Alley" in the US. This is a belt of the American Midwest, particularly Oklahoma, Kansas, Missouri and northern Texas, where every spring, cold, dry air coming down from the Rocky Mountains meets warm moist air coming up from the Gulf of Mexico to produce the spectacular twisters that can devastate communities.
But Britain also sits on a warm air/cool air boundary, at the meeting point of the cold airflow from the Arctic, and the warm airflow from the tropics. The result, says Dr Terence Meaden of Britain's Tornado and Storm research Organisation (Torro) is that Britain has the highest incidence of tornadoes per unit of land area in the world.
That is not to say the UK has more twisters than the US; in some years thousands are reported in America. But we do have more per square kilometre, says Dr Meaden.
His organisation has records of UK tornado frequency and strength since 1960, and these shows a long-running average between then and 2000 of about 33 a year in Britain. (The annual figures can be as low as 15, or as high as 160, as in the exceptional year of 1981.)
But in the past five years, Torro has recorded a big increase in reported British tornadoes, up to between 60 and 70. Does this mean UK tornadoes are suddenly on the increase, and is this perhaps a sign of climate change? Probably not, says Dr Meaden. He thinks it is more a factor of increased publicity and interest, added to much more available recording equipment such as cameras in mobile phones.
In fact, he says, it is not possible to differentiate between a real increase in UK tornadoes in recent years and an increase in the effort in observing them.
A warmer world might be expected to produce more tornadoes, because there will be more heat energy and water vapour in the atmosphere, but there is not the direct link as there is with hurricanes, whose formation is crucially dependent on sea-surface temperature. By Michael McCarthy