Terror offenders due to be released before April have been told they will not be freed under emergency legislation planned by the UK government.
The government said this week that laws to stop the automatic early release of terror offenders will apply to both current and future cases.
The lawyer representing one of six offenders due to be released in March said his client had been told his release date had changed, the BBC reported.
Government ministers are working to get tougher new terrorism laws passed before the automatic release of the next terror offender.
Shopkeeper Mohammed Zahir Khan was due to be released later this month halfway through a sentence for sharing ISIS propaganda online, according to reports.
The government has promised to act to end early releases after two terrorist attacks since November carried out by men who were freed from prison part way through their jail terms.
Sudesh Amman was shot dead by police after stabbing two bystanders in the south London district of Streatham on Sunday. It emerged that armed police teams were following him because the attacker posed a "significant risk" after being freed from prison.
The cases have put the spotlight on the effectiveness of the UK’s anti-radicalisation efforts, particularly in prisons.
Most UK prisoners are automatically freed half-way through their sentences to allow for community rehabilitation and to ease pressure on prison numbers. They can be recalled to serve the remainder of their sentences if they break the law.
The government wants to introduce new laws to ensure that terrorist offenders serve two thirds of their sentence before they are eligible for release, subject to scrutiny of their circumstances. There are more than 220 terrorist prisoners in the UK, according to the latest figures.
The government is seeking to introduce new rules by February 27, the day before Khan’s reported release date.
Lawyers, including a former government adviser, say blocking early releases could lead to legal challenges from inmates.
But the head of UK counter-terror policing backed the government’s plans.
Assistant commissioner Neil Basu said police were “supportive of the government’s plans to strengthen our ability to keep the most dangerous terrorists locked up for longer".
“With 3,000 or so subjects of interest on our radar and many convicted terrorists soon due to be released from prison, we simply cannot watch all of them, all the time," he said.
