Ministers are aiming to pass emergency legislation to block the automatic early release of convicted terror offenders before the next prisoner is freed in three weeks, it has emerged.
Sunderland shopkeeper Mohammed Zahir Kahn, 42, is due to be freed on 28 February after serving half his sentence for encouraging terrorism.
An official said legislation would be introduced to the Commons on Tuesday.
It follows two attacks in recent months by men convicted of terror offences.
On Sunday, Sudesh Amman, 20, stabbed two people on Streatham High Road, south London, before he was shot dead by police.
He had been released from jail 10 days earlier, having served half of his sentence, and was under police surveillance.
Kahn was arrested in 2017 and given a four-and-a-half year sentence in May 2018 after pleading guilty.
He had posted a statement on a Twitter account from the Islamic State group calling for attacks. He also admitted a charge of distributing material designed to incite religious hatred after calling for Shia Muslims to be burnt alive.
The government’s emergency measures, which require backing from Parliament, would postpone his release until the Parole Board has given its approval.
‘First job of government’
But ministers have been warned they face a legal battle over its plans.
An ex-independent reviewer of terror legislation, Lord Carlile, said blocking early release “may be in breach of the law”, while the Law Society of England and Wales said it could lead to more prisoners appealing against their sentences.
But speaking on the Peston programme on ITV, Justice Secretary Robert Buckland said: “This is about public protection – it’s the first job of government to get that right.”
Mr Buckland acknowledged that the measures were likely to be challenged in the court, but maintained the government was taking the right action.
On Wednesday, the head of UK counter-terror policing warned the threat from terrorism was not diminishing.
Metropolitan Police Assistant Commissioner Neil Basu, said security services knew Amman “posed a significant risk”.
“But with 3,000 or so subjects of interest currently 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.
The government is aiming for its law change to clear the Commons by the time MPs rises for recess on 20 February and pass through the House of Lords over the following seven days.