The Times asks experts how large the explosion would have been:

The “patio gas” bomb defused in Haymarket would have generated a fireball the size of a house and a shock wave spreading out over a diameter of at least 400 yards, explosives experts said today.

The propane cylinders and petrol used in the device would have triggered a huge conflagration, as well as causing shrapnel and blast injuries from the exploding car chassis and the nails packed around the bomb, according to Hans Michels, Professor of Safety Engineering at Imperial College, London.

Just one 13kg propane canister — the type sold by Calor under the brand name “Patio Gas” — would release a highly flammable cloud of vapour that would spread over an area of 50 to 60 cubic metres before igniting into a still larger fireball, he said.

“The vapour cloud from one cylinder would fill the order of a big room, and when it ignited the effect would be even bigger,” Professor Michels said. “In addition to the power of the explosion and the shrapnel, you would get a fireball the size of a small house.”

But there’s one huge piece of good news: Expect arrests.

The recovery of the intact bomb will also help forensic scientists to trace the bomb-makers, Professor Michels said. Propane cylinders carry a serial number which can be used to find the point of sale, and isotopic analysis could be used to trace any flour used in the main explosive charge.

Sure, they may have filed off the serial numbers. But maybe not. These guys have proven to be not the sharpest knives in the drawers.

Sheer luck prevented a car bomb from killiing and wounding hundreds of Londoners today.

Officers inspecting the car found 60 litres of petrol on the back seat, gas cylinders and containers holding nails inside, which could have caused “significant injury or loss of life”. The bomb was defused.

One witness said that door staff at the nightclub alerted police after the car was driven into bins last night and the driver ran off.

The witness said the large silver saloon car was being driven “erratically” before the minor crash and that the driver then ran off.

Mr Clarke said that some aspects of today’s bomb attempt “resonated with previous plots” and mentioned nightclubs as a potential target.

But he also said detectives are keeping “an entirely open mind” as to who is responsible and called on the public to remain vigilant.

Yeah, let’s think. Who would want to murder hundreds of people in the nightclub district? Hm. Wait, wait, let me think about it a minute….

LONDON — A judge sentenced five men to life in prison Monday for plotting to attack targets in London, including a popular nightclub, power plants and shopping mall, with bombs made from a half-ton stockpile of fertilizer.

The trial for the first time exposed connections between the defendants and the deadly 2005 al-Qaida-linked attack on the city’s transit system.

That’s right. Keep an “open mind,” because it’s obvious that it could have been the IRA. Or maybe those legendary Jewish terrorists, mad about the way their coreligionists are being treated in England.

What’s that? There are no Jewish terrorists? Well, then it must be one of those Christian terrorists. What? There aren’t any Christian terrorists, either?

Why then, who could it be?

An ICM poll last year indicated that a fifth of Muslims had sympathy with the “feelings and motives” of the suicide bombers in the July 7 2005 attack, although 99% thought they were wrong to carry out the attack.

Of course. It’s that tiny minority of extremists!

Sheer luck stopped the murder of many Brits today. Not MI5. Not the police investigations. Not all of Britain’s work at preventing another major bombing. Luck, and only luck.

They will not be able to rely on luck as a means to prevent more attacks.

Update: Three car bombs have been found so far. There will most likely be a fourth. Classic Al Qaeda methodology.

Update 2: No, only two so far. But really, really dangerous, if they’d been made correctly.