A new blanket ban on legal highs is to be so widely drawn that its provisions could be used to outlaw alcohol, tobacco, coffee and many other widely-used items, ministers have acknowledged.

The Home Office said that one of the main elements of the psychoactive substances bill would be a ban on the trade in “any substance intended for human consumption that is capable of producing a psychoactive effect”, with a maximum seven-year prison sentence to back up the ban.

But it quickly added that “substances such as alcohol, tobacco, caffeine, food and medicinal products would be excluded from the scope of the offence”.

The legislation to be published later this week is modelled on similar blanket bans in Ireland and Poland, but in both cases their legislation specifies that the psychoactive or mind-altering effect must be “significant” so as to exclude commonly-used stimulants.

The decision to ban a whole class of substances, then specify which ones are permitted, is contrary to centuries of British common law under which citizens have been allowed to do or consume anything unless expressly forbidden.

The new legislation designed to ban the new generation of chemically engineered drugs which imitate more traditional illicit substances, such as cannabis and ecstasy, will also be unusual in that it will not criminalise the personal possession of all legal highs. Instead, simple possession of specific substances will continue to be controlled under the Misuse of Drugs Act 1971.

Ireland’s law banning legal highs was introduced in 2010. Since then, police have reported that 102 headshops which sold legal highs and other drug paraphernalia have virtually disappeared.

A recent Home Office study of the impact of the Irish law said that drug workers had expressed concerns about displacement to heroin and prescription drugs, as well as the development of an illegal street market in legal highs. However the number of people attending drug treatment clinics due to abuse of legal highs had declined.