“No dangerous terrorist should be released automatically only to go on to kill and maim innocent people on our streets,” said justice minister Robert Buckland in a statement
Britain will end the automatic early release of convicted terrorists under new fast-tracked legislation to be introduced to parliament on Tuesday.
The legislation follows an attack earlier this month by an Islamist militant just days after he was set free half-way through his jail term, despite authorities believing he still posed a threat to the public.
The government had already promised tougher rules on terrorism after another former convict killed two people and wounded three before being shot dead by police near London Bridge in November.
The emergency measures, which the government wants to become law by the end of the month, will mean convicted terrorists cannot be released before the end of their sentence without an assessment of whether they are still a risk.
"No dangerous terrorist should be released automatically only to go on to kill and maim innocent people on our streets," said justice minister Robert Buckland in a statement.
"Enough is enough. This government will do whatever it takes to keep the public safe, including making sure no terror offender is released early without a thorough risk assessment by the Parole Board."
The government said around 50 people currently in jail would see their release blocked as a result of the change to the law, which will also apply to those sentenced for crimes including training for terrorism and the dissemination of terrorist publications.
Under the new law, they will have to serve at least two-thirds of their sentence before being assessed.
The government said it also plans to boost deradicalization measures in prison, introduce a minimum 14-year term for the most serious terror offenders and increase funding to police to deal with terrorism.