Today's tornado in North West London was a medium-sized twister by British standards. Initial reports of the level of damage to trees, roofs and cars indicate wind speeds of around 100mph (160kph), a T3-T4 strength tornado, on a scale ranging from T0 to T10 developed by the Tornado and Storm Research Organisation (Torro).

In fact, Torro had issued a forecast alert of thunder, hail, lightning and tornado as conditions in the southern half of Britain turned convective. This meant that air was rising through the atmosphere - a surge of warm, moist tropical air rose up and hit colder drier air higher up, exploding into thunderclouds. This produced a squall line, a violent band of thunderclouds, which tore across Southern England during the morning.

Crucial for the development of a tornado, the winds in the atmosphere were coming in different directions and set the air spinning inside a cumulo-nimbus cloud, rather like whirling a child’s spinning top. As a vortex created within, the cloud grew increasingly narrow and spun faster – rather like an iceskater spinning faster as they flatten their arms against their body - until eventually a funnel-shaped cloud grew from the bottom of the thundercloud and touched the ground with violently rotating winds: a tornado.

Such incidents in this country are often incorrectly dubbed "mini-tornados" in the media. In fact, tornados in Britain can be as powerful and destructive as the infamous twisters of Tornado Alley in the American Midwest. In July 2005, Birmingham was struck by one of the most brutal tornados recorded in this country, with wind speeds estimated to have reached over 140mph (225kph), which blasted out shop fronts, ripped off roofs, brought down buildings and felled more than 1,000 trees. Nineteen people were injured and damage was estimated at £39 million.

Coincidentally, tomorrow marks the anniversary 52 years ago of another violent tornado in West and North West London. A huge thunderstorm drove in from the South Coast, the sky turned ink-black and a tornado touched down at Bushey Park, near Hampton Court, smashing down trees.

At around 5pm, the storm reached Chiswick, West London, with a huge conical cloud hanging down from the sky, green lightning flashing from its sides and a deafening roar like an express train. The tornado blew Gunnersbury station apart before demolishing two nearby factories and driving on through Acton, not far from BBC Television Centre, and on to Willesden, close to Kensal Rise. Roofs on houses were ripped off, chimneys crashed down and walls collapsed. A car was reported hurled through the air whilst terrified people outside ran for cover as a barrage of bricks, glass and wood shot through the air like missiles. Newsreels of the day showed a scene of devastation in described as looking like something from the Blitz.

The vortex cut a swathe of devastation for several miles, finally petering out around Golders Green and Southgate in North London. Amongst all this mayhem, it is incredible that there were very few casualties, with only minor injuries.

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