A smoking ban is being considered for prisons across England and Wales.
The Prison Service is due to begin a pilot next year, with the ban implemented by 2015 in the hopes of avoiding legal action by staff and inmates who have suffered from passive smoking.
Smokers would be offered nicotine patches as a substitute.
However, campaigners have warned that a ban would be hard to put in place, and could be destabilising.
An estimated 80% of prisoners are thought to be smokers.
A Prison Service spokesman said: "We are considering banning smoking across the prison estate and as part of this are looking at possible sites as early adopters."
Exeter and Eastwood Park prisons could be involved in the pilot next spring.
The Prison Officers Association (POA) union began campaigning for a smoking ban in all UK prisons in 2007.
It had expressed concerns about staff and prisoners "forced to suffer the harmful effects of second-hand smoke".
Andrew Neilson, from campaign charity the Howard League for Penal Reform, said a ban would be difficult to enforce.
He told the BBC: "Prisons are going through unprecedented budget cuts, prison resources, staff resources have been cut, there may well be good intentions behind this policy proposal, but it will undoubtedly put a lot of pressure on jails which are already pretty stretched."
He added there could be a damaging effect in the short term on the mental health of prisoners "who are often very distressed".