Fortunately it didn't go off.

London escaped what could have been its worst terrorist attack this morning when a car bomb packed with nails, gas canisters and containers of petrol apparently failed to detonate outside a popular West End nightclub hosting a 'ladies' night'.

Police were called to Tiger Tiger nightclub on Haymarket near Piccadilly Circus shortly before 2am when smoke was seen coming from the inside of a Mercedes car parked outside. Unconfirmed reports said that a man had been seen running away from the vehicle.

Inside officers discovered "significant quantities" of petrol, believed to be 60 litres, plus nails and gas cylinders.

The bomb itself was packed with nails to act as shrapnel.

If the device had exploded, police said that the shrapnel would have killed or injured anyone within a wide area. The bomb could have caused a fireball as big as a house followed by a large shock wave.

Deputy Assistant Commissioner Peter Clarke, head of Scotland Yard’s counter-terrorism command, said: "It is obvious that if the device had detonated there could have been significant injury or loss of life."

While later reports question the size of the bomb and the competence of the bomb-makers, it is clear that this was a serious attempt to terrorize London again.

Hot Air has a roundup of coverage, including a mention of the second vehicle which has caused the closure of Park Lane in London -- could there be a multi-bomb plot in the midst of Wimbledon and on the eve of the Princess Diana tribute concert?

MORE AT Michelle Malkin and the Counterterrorism Blog.