A convicted Islamist terrorist who was caught trying to smuggle blueprints into Britain showing how to build a missile has been released from prison early under the Government’s controversial plans to ease prison overcrowding.

Yassin Nassari, a Category A prisoner who was sentenced to three and a half years imprisonment last summer, was released early from Wakefield prison last month, the Ministry of Justice (MoJ) confirmed today.

The disclosure is likely to re-ignite the row over the Government’s early release scheme which is designed to allow “non-violent” offenders out of jail early in order to curb overcrowding.

The move is believed to be the first time that a convicted terrorist has been released under the scheme. The MoJ said that Nassari’s release 17 days early was justified because he had not been convicted of an offence involving “serious violence”.

Nassari, 28 and from Ealing, West London, was jailed for three-and-a-half years at the Old Bailey last July for possession of material that would be useful to terrorists. He had been stopped at Luton airport after getting off a flight from Holland.

In their luggage was a letter his wife Bouchra el-Hor had written urging him to fight “jihad” and saying she hoped their five-month-old son would also be martyred.

She was cleared of withholding information after saying that the letter was a piece of “creative writing” brought on by a failing marriage.

The court heard how Nassari had shared extremist videos with a member of another terrorist cell which provided information over the internet on suicide vests, car bombs, booby traps and poisons.

Police found jihadi material on his laptop and removable hard drive, including blueprints for an Al-Qassam rocket which has been used by the Palestinian terrorist group Hamas.

The files showed detailed measurements and information about the missile and how to make propellant and explosive charge.

Nassari was also the subject of unconfirmed reports last November that he had been moved from Belmarsh prison in South London amid fears that he planned to blow up the jail.

A prison service spokeswoman today denied that his move was linked to a bomb plot. "It is not true that a prisoner was found with information which could have been used to make a bomb. Managed moves routinely take place as part of the high security process," she said.

David Davis, the Shadow Home Secretary, said: “The Government’s perverse approach to security defies common sense.

“On the one hand, they are trying to pass a new law extending the period for holding innocent people - convicted of nothing - when we already have the longest period of pre-charge detention in the free world.

“On the other hand, they are releasing a terrorist we have managed to bring to justice, a dangerous man convicted in our courts for researching how to deploy military weapons in this country.”

An MoJ spokesman said today: “A category A prisoner was released from Wakefield prison on 11 February 2008. The prisoner met the criteria for early release under the End of Custody Licence (ECL) scheme. Where a prisoner satisfies the criteria then release must follow.

“[The National Offender Management Service] can confirm that, in line with normal practice concerning prisoners released on ECL, the Prison Service made arrangements with the relevant police and probation services to ensure that they were aware of his release.

“This individual is subject to licence conditions and multi-agency public protection arrangements.

“NOMS has not been notified of any re-offending by this individual during his period of 17 days on End of Custody Licence or during his continuing probation supervision since then.

“ECL is only available to prisoners whose offences are not considered serious enough by the court to justify a long term of imprisonment. Therefore, only those serving less than 4 years are eligible for ECL.

“Terrorism related offences involving serious violence — such as using explosives to commit GBH or hijacking — are excluded from ECL. "

More than 18,500 prisoners have been freed under the scheme since it was introduced by Jack Straw, the Justice secretary, last June.

They included more than 3,500 violent offenders, 1,730 burglars, 400 robbers and 790 people jailed for drug offences.

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