Last week, Home Office minister Norman Baker resigned from his role after arguing that the government should base its drug policy on evidence drawn from a government-commissioned report. You know, rather than on the whims and hunches of politicians. The study, written by civil servants in the Home Office, showed that criminalising drug possession had no impact on levels of drug use, but the Prime Minister's office said a policy of decriminalisation was "reckless", and Baker – sick of the lack of support for "rational, evidence-based" drug policy – made for the door.

It was the same story that played out in 2009, when David Nutt – then-chief drug advisor to the UK government – was kicked out of his role as chair of the Advisory Council for Misuse of Drugs after saying that cannabis, LSD and ecstasy are less dangerous than alcohol or cigarettes, which they are.

Reacting to Norman Baker's resignation, Nutt told me, "I kind of thought, 'If the minister himself cannot effect change, I was pissing in the wind, wasn't I?' It sums up the problem. Scientists can't make things change, politicians can't make things change. This is a monolith."

It's easy to forget that a rational drug policy would be a holistic thing, but what would that policy actually look like? I asked Nutt – a leading neuroscientist and Imperial College professor who's just completed the first ever brain-imaging study of LSD – to recommend an evidence-based policy for every drug you're ever likely to take.

But first, here are the basics:

Decriminalise possession

David Nutt says, "Using drugs can be a rational choice, a bad choice, or in cases of addiction, a very constrained choice. It is never a crime. Therefore, no criminal sanctions for drug possession and use."

But it can't just be a free-for-all

Just because you're not throwing drug users in prison doesn't mean they're totally uncontrolled. "Drug products, like other risky products, need to be manufactured and sold in ways that manage those risks. Therefore, drug-specific regulations are needed – from light-touch rules to strict pharmacy-only access."

Keep unregulated dealing to a minimum

Nutt is not the dealer's friend: "Personal allowances and administrative penalties for exceeding these may be needed for some drugs, to limit the volumes of drugs in black markets."

No cool packaging or adverts

It's difficult to be "rational" about drugs if you're being blasted with adverts implying that taking pills will definitely help you make friends. "Addiction is an enemy of health and freedom as much as prohibition is," says Nutt. "There must be no room for creating profit at the expense of health and choice. Therefore, prohibitive controls must be targeted at corporations, not consumers, with total bans on the marketing and advertising of products with more than a very low potential to be dependence-forming."

And now that evidence-based drug-by-drug drug policy.

(Photo by John Beck)

ALCOHOL

Put down your can and get reacquainted with your local, assuming it hasn't already closed down. "The massive increase in alcohol harm has been driven by availability in supermarkets in the 1960s and 70s," says Nutt. So the best course of action here would be to reclassify alcohol as a licensed drug – i.e. only available to buy in pubs and other licensed premises, but not supermarkets.

CANNABIS

"Cannabis, frankly, I think you could just sell in cafes like in Amsterdam," says Nutt. So look forward to a proliferation of German teenagers on their first overseas voyage sloping around Edinburgh with barely-open eyes trying to avoid being run over by the tram.

MDMA (Photo by Navmans)

MDMA

You would legally be allowed to get really fucking blissed out and end up snuggling your friends in the bath, but not every single weekend – just most of them. It would be sold over-the-counter in pharmacies and maybe clubs, with regulated access, and a personal allowance of about 50 doses per year.

KETAMINE

For the sake of keeping the nation's collective bladder healthy and functional, K would be entirely unavailable, or possibly regulated as a pharmacy-only medicine in limited amounts, with a daily maximum of one gram.

"Ketamine's a particular problem because when they moved it from [class] C to B they also brought in hundreds of ketamine analogues, many of which have never been made. It's possible there are many safer ketamine-like drugs, but we'll never be able to find them now because they've all been made massively illegal," says Nutt.

(Photo by Chris Bethell)

COCAINE

Also wiped out entirely, because it's not as good as people tend to think. "If we had proper access to drugs like MDMA, mephedrone... stimulants of that class, people wouldn't need cocaine," says Nutt. "It's more toxic than newer stimulants by virtue of its complex pharmacology. I would find it difficult to have a regulated cocaine market."

CRACK COCAINE

Ditto: "If people had a choice, I'd rather they snorted [cocaine] than smoked."

(Photo by Paul Roban)

HEROIN

Available on prescription only. "The idea that you can walk off the street and say, 'I'm going to try my first shot of heroin intravenously, even in a controlled environment' – that's too dangerous. Heroin kills people in hospitals when doctors give it [to them], so I don't think you can have heroin for personal use."

AMPHETAMINES/METHAMPHETAMINE

These would be sold over-the-counter in pharmacies with regulated access and a personal allowance – but only as low-dose pills. So they wouldn't really be all that speedy, unless you took a handful of them, I guess.

Crystal meth would be banned completely. "Smoked methamphetamine is like crack, and smoking stimulants makes you very addicted, very fast," says Nutt. "Methamphetamine is longer lasting than amphetamine, and certainly longer lasting than cocaine. Certainly injecting or smoking methamphetamine is a bad thing."

BENZODIAZEPINES

The sensible approach here would be to sell benzos over-the-counter in pharmacies, with regulated access and a personal allowance. So good news for those of you who enjoy a chemically-induced state of mild sleepiness: the hassle of trying to get hold of rare prescription drugs is nearly at an end (assuming Nutt's proposals are adopted, which isn't looking likely)

Magic mushrooms (Photo by Ysyntu)

MAGIC MUSHROOMS / LSD

Most psychedelics should have pharmacy-only over-the-counter availability with regulated access and an annual limit. "They've never killed anyone, to my knowledge," says Nutt.

TL;DR: You can send your mind off on holiday once a year or so, but not completely lose touch with reality every weekend.

NBOMe-CLASS PSYCHEDELICS

These are currently sold in place of increasingly scarce acid, but they're stronger and therefore much more dangerous. In a rational world, they would likely be unavailable. "The NBOMes are tricky. I presume that the majority of people do it because they're legal," says Nutt. "They are, I think, to LSD like heroin is to codeine."

Some guys in a Kenyan khat warehouse preparing the drug for transportation to the UK

KHAT

The Somali community can breathe easy. In a sane world, there would be unregulated access to khat. "Khat should never have been made illegal," says Nutt. "Khat was only made illegal because the Americans were banging on at us for 15 years to [make it illegal]."

TOBACCO

This would be available over-the-counter in plain packaging from pharmacies, with no limit. In other words, it would be pretty much the same, but you might pick it up from a pharmacy rather than a corner shop and you couldn't base your decision on the pretty coloured cardboard.

In essence, it would still be legal, but also much more like buying some high-strength painkillers, which kind of takes the fun out of it.