Smoking will be banned in all Welsh prisons and four in England from next year to reduce health risks, the Government has said.

The move is the first step towards all jails in both countries becoming smoke-free.

From next month, open prison inmates will not be allowed to smoke indoors and will be restricted to outdoor areas. Plans are also under way to provide voluntary smoke-free areas in all prisons from early next year.

In a letter to Robert Neill MP, chairman of the Justice Select Committee, prisons minister Andrew Selous said the ban would not be rolled out overnight, but that it would be phased in.

He wrote: "Since the introduction of smoking legislation in 2007, our desire has been to move towards smoke-free prisons but, given the high prevalence of smoking and the unique environment of prisons, you will appreciate that implementing smoke-free prisons is a difficult thing to do."

As things stand, prisoners are allowed to smoke in their cells but not in communal areas.

Measures such as e-cigarettes have already been introduced to reduce the risk of exposure to second-hand smoke, while ensuring order and control is maintained.

In his letter, Mr Selous said that recent academic studies commissioned by the National Offender Management Service (NOMS) identified high levels of second-hand smoke in some communal areas.

From January HMPs Cardiff, Parc, Swansea and Usk/Prescoed will be smoke-free, and HMPs Exeter, Channings Wood, Dartmoor and Erlestoke will follow suit in March.

Mr Selous said: "We will continue to take a sensible and considered approach, using the experience of the first prisons to go smoke-free to inform the speed at which we move to smoke-free across our remaining prisons.

"We have no plans to move to smoke-free prisons overnight and will only do so in a phased way that takes into account operational resilience and readiness of each prison. The operational safety and security of our prisons will always be our top priority."

Deborah Arnott, chief executive of health charity ASH, said: "In light of the high levels of tobacco smoke in prisons, we are pleased that prisons in England and Wales will finally be going smoke-free, something ASH has been calling for since 2005. However, the plan only covers England and Wales, and we urge prison authorities in Scotland and Northern Ireland to follow suit."

The Prison Reform Trust said prisoners should still be allowed to smoke outdoors.

Deputy director Peter Dawson said: "Michael Gove has said we should send people to prison 'as punishment, not for punishment'. So there has to be a good reason for denying prisoners a freedom when that is not 'a necessary consequence of imprisonment'.

"A sensible and considered approach to smoking in prisons would leave prisoners with a choice - at least to smoke outside. If that is to be denied to them, there has to be proper support while people give up - not just smoking cessation aids, but increased vigilance for signs of distress that could easily turn into self harm or worse."