Opposition Leader Matthew Guy announced on Tuesday that he would ban Victoria's judges from giving concurrent sentences to people who commit serious violent crimes while on bail or parole.

Mr Guy said the state's Sentencing Act would be amended to keep the "worst of the worst" in jail for longer.

The change would apply to 11 violent offences, including murder, rape, one-punch manslaughter, intentionally or recklessly causing serious injury, aggravated home invasion, car-jacking and armed robbery.

But two of the state's top sentencing experts questioned the policy's effectiveness, given judges already have the power to issue cumulative sentences for serious violent and sexual crimes in Victoria.

Monash University Emeritus Professor Arie Freiberg??? said the opposition had provided no evidence its policy would deter violent offenders.

He warned that removing the judiciary's power of discretion "could lead to grossly disproportionate sentences" being handed down.

For example, someone convicted of committing a string of aggravated burglaries while on bail or parole could receive a longer sentence than a murderer, Professor Freiberg warned.

"You may end up with sentences of 50, 60, 70 years, which may be out of line with sentences we would be imposing for even more serious offences such as murder," he said.

Swinburne University Law School's Professor Mirko Bagaric??? said scrapping concurrent sentences "won't reduce crime" but will increase the state's prison population.

"The most meaningful deterrent to crime is an increase in the perception of offenders that if they do something wrong they will get caught," Professor Bagaric said.

"That's why people don't commit offences at police stations or at airports, because they know they'll get nabbed."

But Mr Guy said he wasn't interested in academics' views about the policy, only in protecting victims of crime.

"I believe very clearly that those people who have committed a serious violent offence when offending on bail or parole, these are the worst of the worst people, they should not be given a soft touch," Mr Guy said.

"They should not be able to get away with more offences on top of what they have already been bailed or paroled for."

Concurrent sentences allow offenders who have committed more than one crime to serve multiple sentences at the same time.

Adrian Bayley, sentenced to 35 years in jail for the 2012 rape and murder of Jill Meagher, is also serving two concurrent sentences of 12 years and nine months for two previous rape convictions.

Mr Guy said removing the option of imposing concurrent sentences would act as a deterrent and deliver a tougher penalty.

He said it would likely apply to between 50 and 200 of the state's worst violent offenders.

He declined to say what the policy would cost but said he expected it would require an increase in the number of prison beds in Victoria.

Attorney-General Martin Pakula said Victoria's bail and parole systems were already being tightened.

The Adult Parole Board's 2016-17 annual report shows there has been a 92 per cent reduction in the number of people convicted of committing a serious violent or sexual offence while on parole over the past four years.

Five parolees were convicted of a serious offence in 2016-17, down from 60 in 2013-14, when former High Court judge Ian Callinan began a review of the state's parole system.

"The Liberals continue to make things up as they go," Mr Pakula said.

"We've already put in place tougher sentencing, we're overhauling our bail system, our parole system is now the toughest in the country, and we'll continue to make the changes necessary to keep Victoria safe."

Members of the Coalition's victims of crime reference group joined the policy announcement, including Janine Greening, whose 73-year-old mother, Marie Greening-Zidan, was murdered and sexually assaulted in her Seaford home by two teen offenders.

Ms Greening said the youths who murdered her mother had later left her threatening and vile messages while inside youth detention.

One of the youths, who cannot be identified due to a suppression order, also offended while on parole, while she was threatened by the youth's family.

Ms Greening said victims of crime should have the right to feel safe.

"I'm for the victims," Ms Greening said.

"If someone has been rehabilitated, fair enough, and they go out to make a better life.

"But if you're not sorry for what you've done, we've got to do something about the people that ??? keep committing crimes."