It is no secret that the Home Office minister Caroline Flint is a tough nut. When she and her boyfriend found themselves in a bank hold-up in 1994, the duo tripped the fleeing gunman, hit him on the head and held him down until the police arrived.

Last week she was experiencing a series of more bruising encounters as she tried to sell the convoluted logic of the government’s plan to downgrade cannabis to the status of a drug no more dangerous than painkillers.

The confused message of this initiative is that cannabis is less harmful than previously thought and those caught smoking it will probably be let off with a caution; hence a £1m campaign to proclaim that the drug is both harmful and illegal. Baffled yet?

Flint, a raven-haired Londoner who became a minister only seven months ago, is unruffled by these contradictions. During our interview, she shrugs off that morning’s condemnation of cannabis by the British Medical Association (BMA)and alarming new evidence of links between it and mental illness.

Behind this apparent disregard for public concerns lurks a larger Home Office agenda that would be instantly comprehensible to the hookah-smoking Caterpillar in Alice in Wonderland but is not easily grasped by normal mortals.

What, for example, is the real reason for the government’s decision to reclassify cannabis from a class B to a class C drug, putting it on a par with painkillers, steroids and tranquillisers? Why open this can of worms, provoking Michael Howard to pledge that a future Conservative government would reverse the legislation?

Flint begins with a patter about police being liberated to tackle hard drugs. “We know the use of class A drugs — cocaine, heroin, crack — causes the most amount of crime. They are also the drugs of which violence is often a common feature, in terms of organised crime and other criminal activity.”

This suggests cannabis users should be left alone because they are too spaced out to disturb the peace. But, paradoxically, her main preoccupation seems to be with explaining the relative “harms” of cannabis and class A drugs to the young. “If we’re going to have an engagement with young people, it has to be one that is honest and credible about the different harms that these drugs pose for them,” she says.

In a month-long campaign in newspapers, radio stations and leaflets, children will be told that hard drugs are more harmful than cannabis, although the latter has health consequences. These facts might seem self-evident to the young who, as the 42-year-old minister admits, “know about drugs because they’re using them”.

Like “totality”, “harms” is one of those words in the government lexicon that has shades of meaning. Flint asserts that alcohol and amphetamines are “worse” than cannabis. But there is no ambiguity about the BMA’s alarm at the drug’s reclassification.

Last week the association said the move, due to come into effect this week, sent out “all the wrong messages” to people thinking of experimenting with drugs.

Another warning comes from Robin Murray, head of psychiatry at the Institute of Psychiatry, who says people who use cannabis in their teens are up to four times more likely to develop psychosis, and that in one study up to 80% of new psychotic cases used cannabis.

When I mention this, however, Flint switches to denial mode. “If people have mental illness problems and they are abusing substances such as cannabis or legal drugs such as alcohol, then there are dangers, particularly if they are not following courses of treatment or other forms of medication that have been prescribed for them.”