"No child ever went to a drug dealer for heroin for their first deal – they would all have started with a bit of weed," said Sidwick, who specialised in the medical application of drugs in his professional career.
"People who call this drug recreational haven't seen the harm that psychosis and other cannabis-related conditions can do, and the costs that heap on our health service and society more generally," he said.
"We aren't just talking about 'a bit of weed' anymore, this does the same harm as crack and heroin. That's why we need the penalties for this illegal gateway drug to match those of class A substances."
'Topsy turvy' legalisation arguments
The proposal is backed by other PCCs including Alison Hernandez (Devon and Cornwall), and Mark Shelford (Avon and Somerset), who will present their plans at the Conservative Party Conference alongside academics and Jamie, a mother whose son James died as a result of his cannabis addiction.
France places cannabis alongside heroin and cocaine on its primary drug list, but most other countries are moving in the opposite direction in liberalising their approach to the drug.
About half of US states have decriminalised or legalised cannabis, allowing its licensed sale to the public, as have three Australian states, Canada, Uruguay, Thailand and most recently Malta. Germany is planning to decriminalise as is Luxembourg.
However, in evidence to the home affairs committee of MPs, Sidwick said the argument for legalising cannabis was "topsy turvy".
"Those advocating it constantly ask for proof of cannabis being negative rather than making a case for cannabis to prove itself a positive addition to society," he said.
'Under constant review'
Like alcohol, cannabis users could gravitate to other drugs and build up a tolerance, requiring them to take more and stronger substances to satisfy their habit.
He cited as evidence a pilot in Lambeth, south London, where cannabis was decriminalised, the hospitalisation for class A drugs increased by 40 to 100 per cent. He said there was also evidence of a 30-fold increase in psychosis in Portugal since it was decriminalised.
Sidwick said any legislative change needed to be allied to an educational drive targeting children from an early age.
"Drug gangs use the term 'Tiny' to describe an infant member and I have been made aware of children as young as 8 acting out drug behaviours as play in the school playground," he said.
"What is needed is a whole system and age view and the passionate commitment of the Department of Education as a partner to address this. There needs to be a societal mission to really engage with this issue and be clear that drug taking is harmful."
The Home Office said there were no plans to upgrade cannabis to a class A drug but illicit substances were kept under constant review.
By Steve Rolles and Niamh Eastwood
'We need meaningful change - but not a ramping up of the same failed punitive prohibitions'
Increasing punishment for the millions of UK cannabis users by reclassifying it as a class A drug flies in the face of all evidence and reason. Rather than doubling down on the multi-generational failures of the war on drugs we should be following the evidence from innovations in the UK and around the world and move in precisely the opposite direction - towards decriminalisation and responsibly regulated legal markets.
The debate around cannabis classification has raged for decades. It was first reclassified from B to C in 2004 on the recommendations of the government's expert Advisory Council on the Misuse of Drugs. But was reclassified back up to B in 2008, against the council's expert advice, showing how the issue has often acted as a lightning rod for public fears, and political exploitation of the drugs issue.
The endless debates around cannabis risks and its classification have often been characterised by cherry-picked evidence in support of a particular position; from reefer madness hyperbole at one extreme to delusional weed evangelism at the other. But such discussions, as well as creating more heat than light, fail to grasp how the problem is not the misclassification of cannabis, but that the classification system itself is a discredited model, a risk-based hierarchy of punitive sanctions that is neither ethical nor effective.
While cannabis classification bounced up and down through the Noughties, levels of use were gradually ticking downwards, seemingly unbothered by Westminster's classification debates. Young people, it seems, do not generally consult the home secretary for drug advice before heading out at the weekend.
Cannabis use is evidently creeping up once again, along with cannabis potency. Despite more than two million criminal records being issued for cannabis offences under the Misuse of Drugs Act 1971 - the use of cannabis has actually risen at least five-fold in the same period.
'Cannabis enforcement drains police resources'
And while drug law enforcement has proven a remarkably expensive yet ineffective tool for reducing cannabis use and related health harms, criminalisation has been shown to cause significant harm, limiting educational and employment opportunities and increasing the likelihood of future offending and problematic drug use.
Searches for cannabis account for at least two out of five all stop and searches conducted in England and Wales. These searches disproportionately impact black and ethnic minority communities, undermining already strained police-community relations. This proposal will not only strain attitudes to police, but will do nothing to prevent problematic use, nor deter crimes from being committed. Just as cannabis enforcement drains police resources, it has, by contrast, empowered and enriched the criminal entrepreneurs who control the multi-billion pound UK trade.
Over 40 jurisdictions around the world have now decriminalised cannabis possession, and many have gone further, with Canada, Uruguay, 19 US states, Germany, Mexico, Luxembourg, Switzerland and Malta among those implementing legally regulated adult-use markets.
We certainly need meaningful change - but absolutely not a ramping up of the same failed punitive prohibitions that have so spectacularly failed for over 50 years.
• Steve Rolles is the senior policy analyst for Transform Drug Policy Foundation,
Niamh Eastwood is the director of Release
