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A former prison governor says the government should consider calling in the Army to restore order in prisons.

Speaking to BBC Newsnight, Ian Acheson admitted the suggestion was "radical" and "controversial" but said "the risks of doing nothing are simply too high".

Mr Acheson said there was a danger a staff member could be murdered.

Earlier, the president of the Prison Governors Association published a damning open letter on the state of prisons in England and Wales.

Media playback is unsupported on your device Media caption "The risks of doing nothing are simply too high" says Ian Acheson

There has been serious violence in prisons in Wiltshire and Hertfordshire in recent days - with riot-trained staff called into the latter earlier this week to restore order.

"There is a systemic and widespread instability in prisons and unless it is tackled, I really do fear that we're going to see a member of staff killed on duty," Mr Acheson told BBC Newsnight.

He said the justice secretary should consider an appeal to experienced staff who have recently left to return, creating a task force to "get back control" in the worst affected prisons.

"If that isn't sufficient, I would suggest that you need extra resources sent into prisons simply to stabilise them short term, and you could consider, for example, using the Army for that."

"It's a very radical measure. It's a controversial measure and it does carry some risk.

"But the risks of doing nothing are simply too high, in my view, to not at least consider - exceptionally and for a short period of time - getting resources onto the landings to restore order and control."

Mr Acheson, who last year led an independent review into Islamic extremism in prisons, lamented what he called the "normalisation of extreme violence".

He said self-harm, suicide, and serious assaults - particularly against staff - are all rising and are at levels that would have been "completely inconceivable" in the past.

Ministry of Justice (MoJ) figures showed a rise in violence in prisons, with 26,643 assaults in the year to March 2017.

Of these, a record 7,159 were attacks on staff - equivalent to 20 every day.

The MoJ insists action had been taken to increase prison officer numbers, but Mr Acheson said this needs to accelerated and that current staffing levels mean staff are "harried, fearful and cannot function effectively".

"There has to be some humility, frankly, from government to say, 'We made a catastrophic mistake here in reducing staff so far and so fast."

He said staff "need help now - not in six months' time" and warned the "consequences would be unthinkable" of not providing this extra support.

But the Director General of the National Offender Management Service and former Director General of HM Prison Service, Phil Wheatley, told Newsnight that sending in the Army would make things worse.

"The prison's ability to handle disorder when it occurs and end that disorder without injury to either staff or prisoner is quite considerable," he said.

"They're really skilled at doing it and they're succeeding in doing that. The army are not trained for that.

"To deploy them in that role would be folly."

Earlier on Wednesday, the president of the Prison Governors Association Andrea Albutt issued a scathing attack on the government's management of prisons in England and Wales.

She said governors had been left "devastated at the complete decline in our service" and that staff faced a "toxic mix" of pressures and an "unacceptable stress and anxiety".

She criticised a recent government reform that separated operational control of offenders from policy decisions as "perverse".