Alcohol is the most dangerous drug in the UK by a considerable margin, beating heroin and crack cocaine into second and third place, according to an authoritative study published today which will reopen calls for the drugs classification system to be scrapped and a concerted campaign launched against drink.

Led by the sacked government drugs adviser David Nutt with colleagues from the breakaway Independent Scientific Committee on Drugs, the study says that if drugs were classified on the basis of the harm they do, alcohol would be class A, alongside heroin and crack cocaine.

Today's paper, published by the respected Lancet medical journal, will be seen as a challenge to the government to take on the fraught issue of the relative harms of legal and illegal drugs, which proved politically damaging to Labour.

Nutt was sacked last year by the home secretary at the time, Alan Johnson, for challenging ministers' refusal to take the advice of the official Advisory Council on the Misuse of Drugs, which he chaired. The committee wanted cannabis to remain a class C drug and for ecstasy to be downgraded from class A, arguing that these were less harmful than other drugs. Nutt claimed scientific evidence was overruled for political reasons.

The new paper updates a study carried out by Nutt and others in 2007, which was also published by the Lancet and triggered debate for suggesting that legally available alcohol and tobacco were more dangerous than cannabis and LSD.

Alcohol, in that paper, ranked fifth most dangerous overall. The 2007 paper also called for an overhaul of the drug classification system, but critics disputed the criteria used to rank the drugs and the absence of differential weighting.

Today's study offers a more complex analysis that seeks to address the 2007 criticisms. It examines nine categories of harm that drugs can do to the individual "from death to damage to mental functioning and loss of relationships" and seven types of harm to others. The maximum possible harm score was 100 and the minimum zero.

Overall, alcohol scored 72 – against 55 for heroin and 54 for crack. The most dangerous drugs to their individual users were ranked as heroin, crack and then crystal meth. The most harmful to others were alcohol, heroin and crack in that order.

Nutt told the Guardian the drug classification system needed radical change. "The Misuse of Drugs Act is past its sell-by date and needs to be redone," he said. "We need to rethink how we deal with drugs in the light of these new findings."

For overall harm, the other drugs examined ranked as follows: crystal meth (33), cocaine (27), tobacco (26), amphetamine/speed (23), cannabis (20), GHB (18), benzodiazepines (15), ketamine (15), methadone (13), butane (10), qat (9), ecstasy (9), anabolic steroids (9), LSD (7), buprenorphine (6) and magic mushrooms (5).

The authors write: "Our findings lend support to previous work in the UK and the Netherlands, confirming that the present drug classification systems have little relation to the evidence of harm. They also accord with the conclusions of previous expert reports that aggressively targeting alcohol harm is a valid and necessary public health strategy."

Nutt told the Lancet a new classification system "would depend on what set of harms 'to self or others' you are trying to reduce". He added: "But if you take overall harm, then alcohol, heroin and crack are clearly more harmful than all others, so perhaps drugs with a score of 40 or more could be class A; 39 to 20 class B; 19-10 class C and 10 or under class D." This would result in tobacco being labelled a class B drug alongside cocaine. Cannabis would also just make class B, rather than class C. Ecstasy and LSD would end up in the lowest drug category, D.

He was not suggesting classification was unnecessary: "We do need a classification system – we do need to regulate the ones that are very harmful to individuals like heroin and crack cocaine." But he thought the UK could learn from the Portuguese and Dutch: "They have innovative policies which could reduce criminalisation." Representatives of both countries will be at a summit in London today, called drug science and drug policy: building a consensus, where the study will be presented.

UK reformers will be hoping the coalition government will take a more evidence-based approach to classification and tackling drugs than Labour did. The Liberal Democrats supported Nutt over his sacking, while Conservative leader David Cameron, who got into trouble at Eton, aged 15, for smoking cannabis, acknowledged the Misuse of Drugs Act was not working during his time as an MP on the Home Affairs select committee.

Nutt called for far more effort to be put into reducing harm caused by alcohol, pointing out that its economic costs, as well as the costs to society of addiction and broken families, are very high. Taxation on alcohol is "completely inappropriate", he said – with strong cider, for instance, taxed at a fifth of the rate of wine – and action should particularly target the low cost and promotion of alcohol such as Bacardi breezers to young people.

Don Shenker, the chief executive of Alcohol Concern, said : "What this study and new classification shows is that successive governments have mistakenly focused attention on illicit drugs, whereas the pervading harms from alcohol should have given a far higher priority. Drug misusers are still ten times more likely to receive support for their addiction than alcohol misusers, costing the taxpayer billions in repeat hospital admissions and alcohol related crime. Alcohol misuse has been exacerbated in recent years as government failed to accept the link between cheap prices, higher consumption and resultant harms to individuals and society."

"[The] government should now urgently ensure alcohol is made less affordable and invest in prevention and treatment services to deal with the rise in alcohol dependency that has occurred."

The Home Office said last night: "We have not read the report. This government has just completed an alcohol consultation and will publish a drugs strategy in the coming months."

A Department of Health spokesperson said: "In England, most people drink once a week or less. If you're a women and stick to two to three units a day or a man and drink up to three or four units, you are unlikely to damage your health. The government is determined to prevent alcohol abuse without disadvantaging those who drink sensibly."Two experts from the Amsterdam National Institute for Public Health and the Environment and the Amsterdam Institute for Addiction Research point out in a Lancet commentary the study does not look at multiple drug use, which can make some drugs much more dangerous – such as cocaine or cannabis together with alcohol – but they acknowledge the topic was outside its scope.

They add that because the pattern of recreational drug use changes, the study should be repeated every five or 10 years.