Poppers will not be outlawed under the blanket ban of legal highs due to come into effect in Britain next month, Home Office ministers have confirmed.

The last-minute reprieve for the liquid chemical drug – technically known as alkyl nitrites – which has been in use as a recreational drug since the 70s follows an outcry among gay people who use poppers to prepare for sex and enhance sexual pleasure.

A former Conservative justice minister, Crispin Blunt, outed himself in the Commons as a poppers user and denounced the proposed ban as “fantastically stupid”.

The decision to confirm the exclusion of poppers from the Psychoactive Substances Act, which will criminalise the trade in legal highs from April, was announced by a Home Office minister, Karen Bradley, on Tuesday.

She said she agreed with the Advisory Council on the Misuse of Drugs that only substances that “directly stimulate or depress the central nervous system are psychoactive”, and should come within the blanket ban on the sale of legal highs.

The ACMD had told the home secretary, Theresa May, that poppers were not only not psychoactive but were also not seen to be capable of “having harmful effects sufficient to constitute a social problem”.

Bradley told the committee: “Having given due consideration, the government agrees with your advice and interpretation of the definition. We do so in the understanding that ‘poppers’ have these unique indirect effects.

“Our understanding is that this approach does not have any further implications for the operation of the Act and that other substances that the Act intends to cover are not affected,” said Bradley, adding they remained confident the courts would uphold the psychoactivity of legal highs banned under the legislation.

The minister confirmed the police and other law enforcement agencies would be asked not to take action against anyone involved in the poppers trade.

The ban on the sale but not the possession of legal highs due to come into force in April is designed to shut down the high street and online “headshop” trade in legal highs, or new psychoactive substances as they are known.

The ACMD says concerns about impaired sight and the risk of lower blood pressure related to use of poppers are rare but should be carefully monitored. There have been a small number of deaths associated with their use, with mentions in 21 reported drug-related deaths between 1993 and 2013.