The UK government’s comparison of international drug laws, published on Wednesday, represents the first official recognition since the 1971 Misuse of Drugs Act that there is no direct link between being “tough on drugs” and tackling the problem.

The report, which has been signed off by both the Conservative home secretary, Theresa May, and the Liberal Democrat crime prevention minister, Norman Baker, is based on an in-depth study of drug laws in 11 countries ranging from the zero-tolerance of Japan to the legalisation of Uruguay.

The key finding of the report, written by Home Office civil servants, lies in a comparison of Portugal and the Czech Republic, both countries where personal use is decriminalised.

“We did not in our fact-finding observe any obvious relationship between the toughness of a country’s enforcement against drug possession, and levels of drug use in that country,” it says. “The Czech Republic and Portugal have similar approaches to possession, where possession of small amounts of any drug does not lead to criminal proceedings, but while levels of drug use in Portugal appear to be relatively low, reported levels of cannabis use in the Czech Republic are among the highest in Europe.

“Indicators of levels of drug use in Sweden, which has one of the toughest approaches we saw, point to relatively low levels of use, but not markedly lower than countries with different approaches.”

Endless coalition wrangling over the contents of the report, which has taken more than eight months to be published, has ensured that it does not include any conclusions.

However, reading the evidence it provides, it is hard to escape the conclusion that the Home Office civil servants who wrote it seem to have been impressed that a health-based rather than a criminal justice-based approach is where effective policies lie.

It also, rather remarkably, says that the experiments in legalisation now under way in the US states of Washington and Colorado, and in Uruguay, should be watched with interest. This is a world away from the “war on drugs” rhetoric that has formed the mainstay of the political debate on drugs in the past four decades.

The report, Drugs: International Comparators, documents in great detail the experience of Portugal, where personal use was decriminalised nearly 11 years ago and those arrested for drugs are given the choice of going before a health “dissuasion commission” or facing a criminal justice process.

“Trend data from Portugal shows how levels of drug use changed in the years following decriminalisation in 2001. Although levels of drug use rose between 2001 and 2007, use of drugs has since fallen to below 2001 levels. It is clear that there has not been a lasting and significant increase in drug use in Portugal since 2001,” the report says.

At the same time, it notes there have been significant reductions in the number of drug users diagnosed with HIV and Aids at a time when drug-related deaths have remained stable: “These outcomes cannot be attributed to decriminalisation alone, and are likely to have been influenced by increases in the use of treatment and harm reduction,” it says, stressing that it is difficult to disentangle the impact of decriminalisation from wider improvements in drug treatment and harm reduction over the same period.

Nevertheless, it firmly rejects claims that decriminalisation in Portugal has led to a spike in drug use. It goes on to contrast Portugal with the Czech Republic, where an evaluation found that there was no significant decline in the availability of drugs following an earlier implementation of stricter laws, prior to decriminalisation.

On the situation in Colorado, Washington and Uruguay, the Home Office says their experimental policies which legalise production, supply and recreational use of cannabis have the common aim of disrupting organised crime and exercising greater control over the use of cannabis.

“The American states have a market-driven approach, with lighter regulation than Uruguay and fewer limitations on consumption and use. Uruguay, which has growing concerns about organised crime, has a stronger role for the state, with limitations in size of the market, the strains and potency of cannabis, and the quantity that an individual can purchase in a month.”

Crucially, the report adds: “It is too early to know how these experiments will play out, but we will monitor the impacts of these new policies in the coming years.”

The report examines various harm reduction initiatives in 11 countries, including the use of drug consumption rooms, the prescription of heroin under medical supervision, and prison-based needle exchange programmes. In particular it found evidence that heroin prescribing, including in three limited trials in Britain, can be effective.

There is no overall conclusion to the report, but in its last paragraph the Home Office authors reflect that the lack of any clear correlation between “toughness” of approach and levels of drug use demonstrates the complexity of the issue: “Achieving better health outcomes for drug users cannot be shown to be a direct result of the enforcement approach.”

• This article was amended on 31 October 2014. An earlier version said incorrectly that, in the Czech Republic, “criminal penalties for possession [of drugs] were introduced as recently as 2010”, and later referred incorrectly to “the implementation of stricter laws in 2010”.