An article in The Times of April 26th 2004 reports the results of a computer model calculating the effects on central Manchester of a relatively minor astroid 45 metres wide.

Within seconds, says the resport, the city would be vapourised and replaced by a crater 3km long.

The explosion would shoot millions of tonnes of rock high into the sky and shower it like bombs more than 30km away.

The blast would trigger a vast fireball followed a split second later by shockwaves with winds of 4,000km per hour so powerful that windows would smash in Bolton.

A severe earthquake would set off seconds later.

It is worth noting however that asteroids hit the earth once every thousand years on average and the chance of one making a hit on Manchester is about once every 5 billion years.