An Islamic terror gang’s plot to attack an English Defence League march failed through sheer incompetence, it can be revealed today.

The attack was to be carried out with loaded sawn off shot guns, homemade bombs - including a firework tube filled with ball bearings and nails – and machetes.

But a devastating atrocity was averted thanks to luck when the gang arrived late - although it leaves the police and MI5 facing serious questions.

A key member of the Birmingham-based extremist Islamic cell had been under surveillance by police and the security service.

Jewel Uddin was linked to another Birmingham al Qaeda inspired terrorist cell who were jailed last week for plotting a suicide bombing attack intended to be “bigger than 7/7”.

Yet together with four other suspects Uddin was allowed to set off last June with their cache of weapons and explosives and head for the EDL rally in Dewsbury, West Yorkshire.

Fortunately they arrived too late and the march had fizzled out when the terrorists reached their terror target in late afternoon.

On their way back to Birmingham two of them were stopped by a routine police checkpoint on the M1 near Sheffield in July last year.

Their Renault Laguna was found to be uninsured and the car was impounded.

But the South Yorkshire police officers failed to properly check the contents of the car and never spotted the deadly cargo in the boot.

Instead the two men were given a lift to nearby Meadowhall station to catch a train home.

Meanwhile the other three who had been travelling in a Rover 25 behind the Laguna were not stopped, but with the armoury now in the hands of the police, they drove home.

The Laguna was taken away and held by a civilian recovery company and it was not until the following day that anyone checked the boot and discovered the haul of arms.

The same day one of the gang actually phoned South Yorkshire police to ask if they could retrieve a bag left in the back of the car.

Six suspects were rounded up and today they all pleaded guilty at Woolwich Crown Court to engaging in conduct in preparation for acts of terrorism.

They will be sentenced in June by the Recorder of Greenwich Nicholas Hilliard QC.

At an earlier hearing, which can only be reported today, the two men in the car were identified as Uddin and Omar Khan, 31.

The three in the Rover were Anzal Hussain, 24 - whose brother was in the other terrorist gang jailed last week - Mohammed Saud and Zohaib Ahmed, both 22.

At that time Ahmed hjad only been released on bail for two weeks after being caught with a document of interest to a terrorist. He later served 14 months imprisonment.

Mohammed Hasseen was in neither car but was arrested when a fingerprint was discovered in one of the vehicles and he was found to be carrying a copy of the al-Qaeda terror manual Inspire.

Prosecutor Bobbie Cheema QC told the court the plot was a “sophisticated and long term planned operation.”

The gang had targeted the EDL march for what it considered to be the right wingers’ blasphemy of the prophet Mohammed.

Forensic scientists found that the weapons were all in working order and the swords had been specially sharpened.

The ammunition was short bird shot which could prove fatal at short range.

The improvised firework rocket device could potentially have caused “significant injury”, the court heard.

Although the short fuse had been left intact the stabilising stick had been snapped off so the rocket would have flown erratically.

Joel Benathan QC, defending said: “When the fuse was lit and the rocket was ignited it would have been random in direction and travel indiscriminately. It would end up highly likely to seriously injure anyone in close proximity.”

He added that although what was created was neither trivial or harmless, its sophistication was “at the bottom of the scale.”