The suspected car bomb discovered outside a central London nightclub has similarities to two of the most significant terror plots discovered in recent years.

A plan to pack cars with propane gas canisters before detonating them at prominent central London locations had been drawn up by Dhiren Barot, an al-Qaeda mastermind.

At about the same time another group of Islamic extremists with links to al-Qaeda was plotting to blow up central London nightclubs with bombs created with fertiliser.

Barot was author of an al-Qaeda terror manual called Rough Presentation for the Gas Limos Project. It sets out in detail a plan to pack limousines with explosives and gas cylinders, park them in car parks beneath buildings and detonate them.

Barot spent a year researching and drawing up the 39-page document before presenting to al-Qaeda planners in April 2004.

He decided to use gas as the main component of his bombs because it was easy to obtain.The 13kg cylinders of Calor Patio Gas discovered in the car abandoned in Haymarket can be bought at hundreds of garden centres across the Britain for less than £20 each.

Barot’s guide says: “Gas can be employed to cause large-scale damage to structures since many of them (gas types) are by nature extremely flammable as well as explosive.”

He researched the burning properties of butane, propane, oxygen and acetylene and the strength of the cylinders in which they were sold. It was essential that the explosion would ignite the gas and shatter the metal cylinders into flying metal fragments.

Barot, 44, further suggested coating the cylinders with napalm and adding petrol cans filled with nails to “further maximise the damage caused”.

Initial reports about the Mercedes discovered in Haymarket suggest that there were hundreds of nails in the back of the car. On the back seat of the saloon car there were petrol canisters, police said today.

Detectives will fear that other car bombs have already been successfully positioned in London and are primed to explode.

Barot envisaged buying three limousines and putting a dozen 47kg (103lb) cylinders of propane in each. The attacks were not planned to be suicide missions, and he wanted an escape plan for his six-man team.

Detectives were unable to identify definite targets for Barot’s plan but found a list of central London railway stations and hotels. The gang had also researched entry points to London and the location of underground carparks.

Explosives and fire experts who studied Barot’s plans said that, although “slightly muddled”, they could be carried out. Charles Todd, of the Forensic Explosives Laboratory, said that it was “a credible plan to make and initiate a very large explosive-incendiary device”.

Seven members of the gang run by Barot were jailed for a minimum of 30 years at the Old Bailey last month for plotting terrorist atrocities on both sides of the Atlantic.

At the same time Barot was planning his Gas Limo Project another group of Islamic extremists were planning to blow up central London nightclubs.

The plot was uncovered by MI5 in February 2004 when they bugged a conversation between Omar Khyam, 24, and Jawad Akbar at a west London flat.

The pair were overheard saying that blowing up nightclubs would “get the public talking”. They discussed taking jobs at a bar or club and detonating a fertiliser bomb on a Saturday night. In particular, they spoke about blowing up the Ministry of Sound in South London.

In the latest suspected attack the car was left outside the Tiger Tiger bar and restaurant in Haymarket, It a well known nightspot popular with young City businessmen and women, Premiership footballers and minor celebrities.

The fertiliser bomb gang justified attacking nightclubs because the customers would clearly be breaking strict Muslim laws on dancing and drinking.

In a tape played to the jury at their Old Bailey trial Akbar, 22, is heard saying: “No one can even turn around and say, ‘Oh, they were innocent’ those slags dancing around.

Khyam asked him: “If you got a job in a bar or club, say the Ministry of Sound, what are you planning to do there?"

Akbar replied: “Blow the whole thing up.”

The pair and three other men bought 600kg of ammonium nitrate fertiliser from an agricultural merchants to create a massive bomb. They were found guilty of conspiring to cause explosions likely to endanger life and were jailed for life in April.

It emerged after the trial that Mohammad Sidique Khan, the leader of the 7/7 bombers, had been spotted on four occasions in 2004 with at least one of the fertiliser bomb conspirators.

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