Boris Johnson has indicated violent or sexual offenders could remain locked up for longer if he becomes prime minister.
The Tory leadership hopeful said it was wrong that prisoners were routinely let out after serving just half of the sentence handed down in court.
Mr Johnson also said Theresa May had been wrong to introduce curbs on the police’s stop and search powers, and said it was important to “change that balance back” in favour of officers.
But while he struck a tough tone on law and order, Mr Johnson hinted to the Daily Mail he could grant an amnesty for long-term illegal migrants.
Setting out his views on sentencing, the former London mayor told the newspaper: “I’m afraid there are too many people, because of the way the sentencing law works, who have committed serious violence or sexual offences who are being let out, as the law prescribes, after they’ve served only half the sentence that is pronounced in open court.
“This is happening. And I’m talking about serious sexual or violent offenders.
“And I think the public is noticing this, quite properly. They don’t think it’s right, and I don’t think it’s right.”
Mr Johnson promised a “relentless focus” on knife crime and criticised the 2014 measures on stop and search brought in by Mrs May.
“When it comes to stop and search, the fact is that we went wrong when we decided to change the rules on the best use of stop and search.
“We made it more difficult. And I think it’s important that we change that balance back.”
Mr Johnson has already pledged to spend £1.1 billion a year funding 20,000 extra police officers as part of his pitch to Tory members to elect him as their leader on July 23.
Are we really, as a society, going to go around telling people who put down roots, who have children, who might have grandchildren here, 'You know, I’m sorry, you’re going home because of the circumstances in which you came'?
On the prospect of an amnesty for migrants who have been living illegally in the UK for at least 15 years, Mr Johnson said as long as they have “played by the rules” while in the country they might be allowed to stay.
“Are we really, as a society, going to go around telling people who put down roots, who have children, who might have grandchildren here ‘You know, I’m sorry, you’re going home because of the circumstances in which you came’?
He said more should be done to keep out illegal immigrants and the authorities should be “very strict” in repatriating those who arrive.
“But I think if people have been here for a very long time, and they haven’t fallen foul of the law and they have played by the rules, all I will say is we should look at it.”
Mr Johnson’s hopes of becoming the next prime minister received a boost as a poll of Tory members suggested he was on course for a comfortable victory over Jeremy Hunt, with three-quarters of Conservatives supporting him.
Mr Johnson is backed by 74% of Tory members against 26% for Mr Hunt, according to a YouGov poll for The Times, carried out between July 1 and 5.
Mr Hunt acknowledged “Boris has been way out the frontrunner” but he urged members to delay casting their ballots until after next week’s TV set pieces – an ITV debate on Tuesday and in-depth BBC interviews on Friday.
It is already too late to win over some Tory members, whose ballot papers have already been filled in and returned to party HQ.
Mr Hunt told The Times: “The big message I want to give to Conservative Party members is wait to see me and Boris in action on the TV debates.
“Try before you buy.”
The Foreign Secretary said there was “a lot of switching going on now they’ve got the bigger picture, that’s causing people to think – yes. they want Brexit, but they want a vision beyond Brexit”.
In the YouGov poll, 90% said they believed that Mr Johnson would force through a no-deal Brexit, while only 27% thought Mr Hunt would.
Some 67% of members think that it would be acceptable to suspend Parliament – something Mr Johnson has refused to completely rule out – to stop MPs blocking a no-deal Brexit.
An overwhelming majority – 77% – think that Mr Johnson’s private life is not relevant to whether he would make a good prime minister.
The former foreign secretary again refused to answer questions on the issue at a hustings on Friday when he was asked by a member whether a good prime minister needed to be “a loyal husband and father”.
The female Tory member who asked the question said that his refusal to answer meant voters would “come to their own conclusion and it may not be a favourable one”.
Mr Johnson said: “Then I’m going to have to live with that.”
Mr Johnson split from his second wife Marina Wheeler, with whom he has four children, last year, after a turbulent 25 years of marriage.
His subsequent relationship with Carrie Symonds threatened to derail his Tory leadership bid, after police were called to a late-night row at their home.
In his Daily Mail interview, Mr Johnson was asked whether Ms Symonds would have an influence on policy if he became prime minister, but he said: “I will be deciding what we do – and I will be getting on with it.”