A prison staff spokesman has given a cautious welcome to a ruling which could see inmates and guards prosecuted for flouting smoking laws.

It means jails will be subject to the same ban which applies to lighting-up in public places in England and Wales.

The government had argued that as Crown premises, state prisons were exempt from smoke-free legislation.

The case went before a judge after an inmate complained about the health impact of passive smoking.

Michael Rolfe, Prison Officers’ Association representative for London and Kent, who also works at HMP Elmley, said: “We’ve campaigned to have prisons no-smoking because of the potential harm to our members.

"Obviously, it’s a very hard policy to enforce with a ratio of approximately 30 prisoners to every member of staff.”

Exemptions to the Health Act 2006 mean that smoking will still be allowed in cells with the door shut where the smoker is 18 or over.

"Inmates are also permitted to light-up in designated outside areas such as exercise yards. The new ruling does not take effect until Justice Secretary, Chris Grayling, has been given time to lodge an appeal.

Lawyers for the minister had argued that the sanction of withdrawal of privileges was sufficient to deal with incidents of unauthorised smoking.

With an estimated 80% of the 84,000 inmates at prisons in England and Wales thought to be smokers, Mr Rolfe said it would be very hard to cut risks associated with second-hand smoke.

He said he would be holding discussions with the National Offender Management Service (NOMS) about the court’s enforcement.

“We welcome this landmark ruling as a leverage to work with NOMS to be able to evaluate the risks of passive smoking to prisoners and staff alike,” he said.