Mr Clark introduced a law to Parliament on Wednesday with ''baseline sentences'' for a number of serious crimes, which he said would specify not only the maximum, but also the ''average or median sentence that Parliament requires the courts to apply''.

''At present, the average sentence imposed for some of these offences is appallingly inadequate,'' Mr Clark said. ''Cases that are more serious than average will be required to receive a higher sentence than the baseline, and cases that are less serious than average will be able to receive a sentence lower than the baseline.''

Mr Clark said the average sentence for a range of serious offences would be increased under the law, including raising the average sentence for murder to 25 years and doubling the average sentence for trafficking a commercial quantity of drugs of dependence to 14 years.

This contrasts with the council's recommendation in a 2012 report that the baseline sentences for those crimes to be set at 20 and nine years respectively.

Rises for other crimes were in line with the council's recommended sentences, including the average sentence for sexual penetration of a child under 12, which will rise from 3½ years to 10 years.

The reforms come as Victoria's prison population reaches record levels. Ombudsman George Brouwer last week warned that the state's dangerously overcrowded prisons would increase prisoner deaths and violent incidents.

Liberty Victoria's president, Jane Dixon, SC, said harsher sentences would further add to the prison population and could make the community less, not more safe.

''Any move towards mandatory sentencing, where judges have less discretion, represents a failure to respond appropriately to the problem of crime,'' Ms Dixon, a criminal barrister, said.

''In the long term this also increases the rate at which institutionalised prisoners are released back into the community.''

She said that the Director of Public Prosecutions could already appeal every sentence imposed in the County and Supreme Court that they thought was ''too low'' to the Court of Appeal.

Liana Buchanan, executive officer of the Federation of Community Legal Centres, said baseline sentences ''undermined the principle that the court, who hears all the facts of the case, is best place to impose an appropriate sentence.''

The Sentencing Advisory Council's chief executive Cynthia Marwood declined to comment.