Boris Johnson says a Conservative government will end the early release of prisoners convicted of terrorist or extremism offences in the wake of the London Bridge terror attack.
As he pushed security into focus during the remaining weeks before the general election, Mr Johnson said it would be part of a tougher action plan on security and crime which will see "terrorists serve every day of their sentence, no exceptions".
As the political row intensified after the attack, Jeremy Corbyn said police should be able to use "whatever force is necessary" if they believe innocent lives are at risk.
It comes as it emerged that Usman Khan, who carried out the knife attack on London Bridge on Friday, was a convicted terrorist who was wearing an electronic tag after being released half-way through a 16-year prison sentence for plotting to bomb the London Stock Exchange.
The sentence was quashed at the Court of Appeal in April 2013 and he was given a determinate 16-year jail term, with a five-year extended licence period, under legislation which meant he was released automatically halfway through the sentence.
Sentencing law changed in 2012, and if Khan was given the same sentence today, he would have had to serve at least two thirds and be released only if the Parole Board agreed.
Even though the law change came into force before Khan's appeal, he could only be sentenced under legislation in force when he committed the offences.
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The Parole Board said it had no involvement in his release and that Khan "appears to have been released automatically on licence" halfway through his sentence.
However, the Ministry of Justice said the licence conditions of every terrorist offender are being reviewed.
A spokesman said: "Work is already advanced on reviewing the licence conditions of every terrorist offender, making sure conditions are as tough as they need to be. We are also stepping up our already frequent meetings with these offenders."
The department said the review was being undertaken to "guarantee public safety rather than because of any particular concern".
Mr Johnson said automatic early release must end and other laws must change to strengthen security – policies that have been inserted into the Conservative manifesto ahead of the general election on 12 December.
Mr Johnson said: "Since becoming prime minister I've said we need a big change of direction on violent crime and security.
"What I have seen over the last 24 hours has made me angry – it's absolutely clear that we can't carry on with the failed approaches of the past.
"This is why I've also said that we must keep violent offenders and terrorists in jail longer and end the automatic early release system."
He claimed that because the "broken hung parliament was preoccupied with blocking Brexit", the Government was unable to make the changes required to keep violent offenders and terrorists in jail for longer.
"This system has got to end – I repeat, this has got to end, as I've been saying for four months."
"If you are convicted of a serious terrorist offence, there should be a mandatory minimum sentence of 14 years — and some should never be released.
"Further, for all terrorism and extremist offences the sentence announced by the judge must be the time actually served — these criminals must serve every day of their sentence, with no exceptions.
"These simple changes, in line with what I've been saying since becoming prime minister, would have prevented this attack.
"If we're going to keep dangerous people in jail longer, we need more prison places.
"This is why I announced in August that we would urgently create more prison places and this is already underway."
Mr Johnson slammed human rights laws which he said the public did not agree with.
He went on: "In our manifesto a week ago, I set out how we must reform human rights laws to shift the balance in favour of our security and intelligence services.
"Many human rights lawyers attacked this move. They are wrong and the public does not agree with them.
"Our laws are constrained, for example, by the "right to private life" which limits surveillance of terrorists and recent court cases have placed unacceptable limits on our intelligence services.
"From surveillance and operations to sentencing and licensing conditions, we must shift the balance of the whole legal system in a much tougher direction against serious criminals and terrorists."
As the political fallout over Friday's attack began to intensify last night and now looks set to become one of the battlegrounds in the general election.
Mr Corbyn is due to speak later on Sunday when he will say: "Real security requires calmly making the right calls at moments of high pressure.
"I will always do whatever is necessary and effective to keep our people safe.