The convicts, all jailed between 2004-2006, are set for release, prompting fears over potential threats to national security.
Security chiefs believe they could form a terror alliance with around 400 battle-hardened radical Islamists across the UK who have returned from Syria and Iraq after fighting for ISIS.
The news comes just days after deranged jihadist Khalid Masood savagely ploughed down four people on Westminster Bridge before stabbing PC Keith Palmer to death.
Former Labour Cabinet minister Liam Byrne warned about the potential risks of “lone wolf attacks” from ISIS terror cells.
He told the Mirror: “Put all this together and it’s the perfect storm.
Security chiefs have warned the prisoners could join ISIS fighters in Britain
“ISIS used to urge people to go to the Middle East to build its sick Utopia. Now it is inciting lone wolf attacks, specifying weapons and targets.”
Messages prompting jihadis to perform such attacks are being disseminated via social media and Rumiyah, ISIS’ propaganda magazine.
The twisted magazine even informed readers about what the most vulnerable parts of the body are and what length of knife is best for killing in last year’s October issue.
Masood is believed to have been radicalised during his time in prison
Warped fanatic Masood murdered police officer Keith Palmer, 48, on Wednesday by stabbing him under his arm, where his stab vest did not protect him.
The depraved 52-year-old then aimed for Palmer’s neck.
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Masood was not on MI5’s radar when he carried out the attack, despite being investigated by the intelligence service in the past for links to Islamist extremists.
The victims killed by Masood include PC Keith Palmer, Aysha Frade and Kurt Cochran
A Whitehall source told the Mirror: “There was no intelligence to justify an investigation.”
Community leaders have argued Masood’s evil killings highlights how more criminals are being radicalised in British prisons.
Masood's attack left four people, including a police officer, dead London mourns terror attack at vigil Fri, March 24, 2017
The world grieves after an attacker killed three people and injured about 40 near parliament in London.
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Floral tributes are left after the vigil in Trafalgar Square, London to remember those who lost their lives in the Westminster terrorist attack
Mohammed Khaliel, director of Islamix, said authorities need to do more to prevent convicts committing lone wolf atrocities after being released from prison.
He said: “It’s well known that some converts are more likely to misunderstand their new religion and then be used by evil forces to carry out atrocities.”