Rapists and murderers could face longer prison sentences under a review launched by Boris Johnson today.

It will investigate if serious offenders should be jailed for longer by changing the law to stop some being let out mid-sentence.

The prime minister said the move, which is part of a series of announcements to crackdown on crime, would help ensure confidence in the system.

But critics warned there was no evidence that longer sentences would result in a reduction in crime and they could be potentially worse for public safety.

Mr Johnson has already pledged 20,000 extra police officers, an extension of stop and search powers and more prison places since entering Number 10 last month.

His latest move is to create a review team on sentencing for violent and sexual offenders and the law around how they are released, to report back in the autumn.

Around £85m is also being gifted to the Crown Prosecution Service to help it manage the caseloads over the next two years.

Mr Johnson said dangerous criminals should be serving the sentences they deserve.

To ensure confidence in the system, the punishment must truly fit the crime, he added.

We have all seen examples of rapists and murderers let out too soon or people offending again as soon as they’re released. This ends now.

Offenders sentenced to 12 months or more currently serve the first half of their time in prison and the second on licence in the community, where they can be recalled.

The review will consider whether changes to legislation are needed so that more time is spent in jail.

On Monday, Mr Johnson will host leaders from the police, probation and prison sectors to discuss how to improve the criminal justice system.

But the risk of rising jail populations was raised by the Prison Reform Trust’s head of policy, Mark Day.

He said British judges give out more life sentences than any other country in Europe and that there has been sentence inflation over the last few decades.

Speaking to Sky News, Mr Day said there was no serious attempt by Mr Johnson’s review to address those issues, which led to overcrowding in prisons, a lack of resources and greater safety concerns.

He warned prisoners released early are supervised and integrated back into communities for the remainder of their sentences.

If we have a situation where serious and violent offenders are actually being released much closer to the end point of their sentence, that means that they’re going to be spending less time in the community under supervision, Mr Day said.

So that could be potentially worse for public safety, if it isn’t done very carefully.

Louise Haigh, Labour’s shadow policing minister and a former special constable, told Sky News on Sunday the criminal justice system was on its knees after nine years of austerity.

She said the courts system, cuts to legal aid and privatisation of the probation service all needed reform.

Carl Cattermole, a former inmate and author of Prison: A Survival Guide, told Sky News: Prison is not a functional way to solve the problem of crime. It’s just not going to solve the core issues of people’s offending behaviour.

However hard you make a jail sentence it’s not going to put people off when the causes of their actions are often mental unwellness or straight poverty.

Liberal Democrat justice spokeswoman Wera Hobhouse said: For years, Labour and Tory ministers have made sentences longer and longer, without any evidence that they prevent crime.

It may sound tough, but it hasn’t made our communities any safer. All it does is overcrowd our prisons and waste millions of pounds.

We do need a sentencing review, but its aim should be to reverse decades of pointless sentence inflation. Instead of just talking tough, it’s time ministers look at the evidence.

(c) Sky News 2019: Boris Johnson: Rapists and murderers let out too soon – this ends now