"If it ain't broke, don't fix it" summed up the response from the Home Office, and later David Cameron, to the publication of the home affairs select committee's year-long inquiry into drug policy last week. Why waste time on setting up a royal commission into drug policy (something his coalition partners, in contrast, went on to call for) when our current drug policy is working? The key evidence for this, quoted like a mantra by the government, is falling drug use. But the "falling drug use" plank on which the government is walking is a very shaky one.

For sure, drug use has been falling since its peak in 2002, although that was after a significant rise spread across the previous two decades. According to the British Crime Survey, in 1996 just over 11% of adults had used an illegal drug in the past year. By 2002 it had peaked at just under 12%. In 2012 the figure sits at just under 9%.

However, Britain is not a nation that has simply fallen out of love with illegal drugs. Drug use remains both higher than in 1990 and than in the rest of Europe and by no means are we witnessing a decline in use across the board.

The prime mover behind the downward trend is cannabis, the most popular illegal drug. Its decline (10.9% of people had used it in the previous year in 2002 compared to 6.9% now) in popularity, especially among young people, has come at a time when the cannabis market has become saturated by the vastly more potent skunk. Combined with the smoking ban, cannabis appears to be a drug going out of fashion, consumed in a way which is (increasingly) socially unacceptable. Yet this is not a result of the domestic policy of this or any other government, it is a Europe-wide trend that has been going on for more than a decade.

Class A drug use is higher than it was 15 years ago. Despite falling from a peak in 2002, ecstasy and cocaine are still vastly popular drugs taken by many thousands of people in a wide range of venues, with anywhere between one quarter and a half of club-goers estimated to take illegal drugs on a night out.

The established dance drugs have been joined by a growing array of new and increasingly popular substances such as mephedrone, ketamine, GHB/GBL, as well as scores of legal highs.

The increasingly widespread use of mephedrone is turning the cheap, easily available and potent stimulant into an "everyman drug", with pockets of popularity across the UK ranging from teenagers to injecting heroin users. Combined as it is on a night out with an expanding menu of legal and illegal highs, and with many users having little idea of exactly what white powder they are consuming – even mephedrone has a plethora of street names – it is now ever harder for surveys to accurately identify trends in drug use.

In fact, despite the welcome news that heroin use is falling among young people, in parts of the north-west including Greater Manchester and Cumbria, crime statistics attest to a significant increase in heroin-related acquisitive crime such as burglaries, bicycle thefts and vehicle thefts, and recessions do not bode well for problem drug use.

In an age of online drug retailers selling an alphabet soup of legal and illegal substances, we don't even know what the future holds and complacency in the face of falling cannabis use is a risky strategy. Heroin, ecstasy, and most recently mephedrone, blindsided the government, the police and even some frontline drug workers. But what we do know from our own research is that the UK appetite for psychoactive drugs remains resilient and thus sustains an illegal market back to Afghanistan, Colombia, China and Peru.

Moreover, drug use is not the only measure of how the drug trade impacts on our children. A quarter of all people convicted of supplying Class A drugs in Britain are 21 or under and the number of teenage drug dealers arrested, charged and locked up for drug dealing is rising every year.

Within hours of the publication of the select committee's inquiry, government officials had already dismissed the report's major recommendation – to urgently re-examine failing drug laws – out of hand. This is despite an agreement made in the wake of David Nutt's sacking from the Advisory Council on the Misuse of Drugs, for government to "demonstrably allow for proper consideration" of scientific advice.

The government's attempts at using the fig leaf of falling drug statistics to hide persistent political inertia is ridiculous. Are not the huge social, financial and health costs to society of the status quo enough to warrant more than a cursory glance? When the official statistics begin to rise again, as they may well do, will David Cameron promise to open the drug policy attic and investigate, or will there merely be calls again to get "tougher" in the war on drugs?