Fairfax Media can reveal that despite mandatory sentences being in place since 2014 for select violent offences, not a single Victorian judge has applied the minimum jail term except on appeal.

The revelations come weeks before minimum sentences for aggravated carjackings and aggravated home invasions, which passed the Parliament this year, are due to take effect.

One of the men who escaped a four-year minimum sentence for "gross violence" was 28-year-old ice user Karl Peter Ravenhorst​, who chased down his 51-year-old victim on a highway in 2014, and bashed him repeatedly with a baseball bat while the man lay in a ditch by the side of the road.

The victim suffered a fractured skull in the assault, which left him with shattered bone fragments embedded in his brain. He has permanent brain injuries.

But Justice Terry Forrest, in sentencing, said there was a "special reason" that would allow Ravenhorst to avoid a minimum sentence – the fact that Ravenhorst had agreed to give evidence against the woman who put him up to the assault.

Had he not pleaded guilty and offered to become a witness, Justice Forrest said, Ravenhorst would have received 10 years, with seven to serve before parole.

Judges can invoke a wide range of "special reasons" to bypass mandatory sentences that apply for some crimes. Judges in the County Court have used these six times since January 2014, according to figures compiled by Court Services Victoria for Fairfax; they have been used twice in the Supreme Court.

The reluctance of judges to slap offenders with the minimum sentences created for serious assaults highlights the schism between politicians talking tough on law and order, and judicial practice.

Mandatory sentencing has been extremely unpopular with the legal fraternity, with the Sentencing Advisory Council, Law Council of Australia, Law Institute of Victoria and others speaking out against the practice.

They argue mandatory sentencing can act as a disincentive to offenders pleading guilty, can deliver sentences disproportionate to the individual offending circumstances, and does not take into account the individual circumstances of offenders.

The Coalition government introduced minimum sentences for "gross violence" in 2013, including intentionally causing serious injury (in circumstances of gross violence) and recklessly causing serious injury (in circumstances of gross violence).

Mandatory sentences also apply for manslaughter in circumstances of gross violence, manslaughter by a single punch or strike (in certain circumstances), and assaults against emergency workers who are on duty.

But at least one mandatory sentence has been imposed on a violent offender, after the Director of Public Prosecutions appealed the man's original sentence.

That offender was Graham Miles Hudgson, who in 2015 was sentenced to 23 months' jail and a two-year community corrections order, for bashing a neighbour with a hammer, after running a campaign of intimidation against the neighbour (including threatening the rape of the man's girlfriend).

The DPP appealed his sentence, and in October the Court of Appeal jailed Hudgson for the mandatory four years.

But the judges reviewing Hudgson's case, Justices Mark Weinberg, Simon Whelan and Phillip Priest, raised serious concerns about minimum sentences, saying "the entire sentencing process becomes problematic, and unorthodox" when judges are forced to apply inflexible sentences.

"A sentencing judge may have to start with the non-parole period, and work upwards from there, rather than imposing an appropriate sentence and then deciding what proportion of that sentence should be served before being eligible for parole," the judges said.