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Urgent changes were made to the Government’s early-release scheme for prisoners last night after the disclosure that two terrorists had been freed before the end of their sentences.

The two releases are embarrassing for ministers. Next week Parliament is to debate giving police powers to detain terrorist suspects for up to 42 days.

Jack Straw, the Justice Secretary, banned future terrorist releases under the end-of-custody licence (ECL) scheme — aimed at easing prison overcrowding — after Times Online revealed that Yassin Nassari, 29, a Category A inmate described by counter-terrorist sources as a “committed extremist”, was freed from Wakefield jail last month. He was convicted of smuggling missile blueprints into Britain.

The Times has also learnt that another terrorist inmate was freed early in January from Glen Parva young offender institution. Abdul Patel, 18, was jailed for six months last year for possessing an explosives manual.

The Ministry of Justice confirmed that Mr Straw had known of the early releases before he announced the reform of the scheme.

A justice ministry spokesman said: “The number of terrorism-related cases likely to fall within the current ECL criteria is very small. However, in the light of these cases the Justice Secretary has decided to change the criteria for the ECL scheme so that any prisoner convicted under terrorism legislation would not be eligible.

“He did know about the release of the prisoner on February 11 before today but ministers needed to apply the criteria in individual cases as they existed at the time. The National Offender-Management Service has not been notified of any reoffending by these individuals during their period of end-of-custody licence.”

Nassari, who went to Syria in 2005 to work as a teacher, was arrested in May 2006 with his wife, Bouchra el-Hor, 24, and their baby as they arrived at Luton airport on a flight from Amsterdam. He was under suspicion because of his links to a number of other extremists and police seized an external computer hard drive from his luggage before releasing the family to return to their home in Ealing, West London.

Examination of the computer equipment uncovered drawings for the construction of al-Qassam missiles and rockets, devices made by Hamas and used in attacks on Israel, and the couple were re-arrested.

The computer drive also contained a library of extremist material including graphic footage of terrorist attacks and the beheading of Western hostages and literature with titles including Preparing the Fighter who is Going for Jihad and Virtues of Martyrdom in the Path of Allah. Further investigations revealed that Nassari had also been in contact with other extremists on the internet using the name Mock Turtle.

A letter from his wife, found in his possession, appeared to be encouraging Nassari to become a martyr. It read: “I am so proud of my husband. I am happy that Allah has granted you the chance to be a martyr . . . Maybe one day I can follow you. If I can’t, I will send our son to you so he can follow his father’s footsteps.”

At their trial at the Old Bailey last year, Ms el-Hor, who is Dutch, said that the letter was a work of fiction. She was acquitted by a jury of charges of failing to disclose information about terrorism. Nassari was convicted of possessing information likely to be useful to a person committing or preparing an act of terrorism and was jailed for three and a half years.

With standard remission and having spent more than a year on remand before his trial, he was due for release at the end of February.

Patel was jailed after a trial at the Old Bailey last September. Police found in his possession a manual written in 1990 to teach US agents how to defuse bombs. It was described in court as “a step-by-step guide” to the manufacture and production of “home-made bombs”. He was due for release in late January but was freed 18 days early.

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