The Government is fighting to pass an emergency law to prevent the automatic release of further terrorists before another is due to walk free.
Just one day later, Sunderland shopkeeper Mohammed Zahir Khan, who was jailed for four-and-a-half years in May 2018 for posting messages and material that was supportive of Islamic State (IS) on social media, is due for release.
The father-of-one, originally from Birmingham, had served long sentences in the past for drugs supply offences and moved to the north east to make a break from gangs.
It is understood that around five others are expected to be let out in March unless the new law is in force.
Meanwhile, Metropolitan Police assistant commissioner Neil Basu, head of UK counter-terror policing, said the "threat is, despite our best efforts, not diminishing", after a third attack in as many months.
The UK's terror threat level is currently set at "substantial", meaning an attack is likely. It was downgraded from "severe", the second highest rating, in November, shortly before the London Bridge attack.
Convicted terrorist Sudesh Amman wore a fake suicide belt as he grabbed a knife from a shop in Streatham High Road on Sunday, before stabbing two bystanders.
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The 20-year-old had been jailed for possessing and distributing terrorist documents in December 2018, but was freed automatically halfway through his sentence less than a fortnight ago.
He was put under 24-hour police surveillance on his release after it is understood security services regarded him as an "extremely concerning individual”.
Mr Basu said: "Police and the security services knew the attacker posed a significant risk and we were, unfortunately, proved right in our decision to place him under surveillance.
"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 welcomed plans announced on Monday by justice secretary Robert Buckland, who said the urgent legislation was needed to make sure offenders serve two thirds of their sentence before they are considered eligible for release, at which point their case would be considered by a panel of specialist judges and psychiatrists at the Parole Board.
There are 224 terrorists in prison in the UK, with most thought to be holding Islamist extremist views, according to the latest published figures to the end of September.
As many as 50 terrorists could be freed from jail this year, figures suggest.
The government plans to introduce the legislation in the Commons on Tuesday next week, with the aim of clearing the House by the time it rises for recess on Thursday.
The bill will then go to the Lords on 25 February with the aim of getting royal assent on 27 February.
The government has not ruled out derogating, effectively suspending, the European Convention on Human Rights (ECHR) in order to apply the new measures.
Lawyers have warned the move would open the government up to legal challenges from those already behind bars who were sentenced under the current rules.
But officials said they are confident they have the flexibility to change how an offender serves their sentence, by extending the time they spend behind bars rather than on licence.