Michael Spurr was speaking to Sky News after a 12-hour riot involving up to 600 inmates at HMP Birmingham that saw staff losing control of four wings at the prison.

Specialist riot squads were sent in to take back control of the prison, which has a capacity of 1,450, after inmates stole keys and lit fires.

The Ministry of Justice has said it is moving 240 inmates out the jail and that additional staff have been brought in to maintain calm.

Mr Spurr, the head of the National Offender Management Service, which runs the prisons and probation service in England and Wales, admitted many prisons are facing problems and that it is going to take "some time" to turn things around.

He told Sky News: "It is quite right to say that we have got serious issues across our prisons.

"What has happened is we have got more prisoners who are more prone to serious violence - gang-related violence, very often.

"We have had a huge influx of illicit, psychoactive drugs that have been pushed into prisons - and those drugs have changed the dynamic in prisons.

"We are doing a great deal to prevent that from happening.

"It is the case that we need more staff to be able to manage the situation in prisons, but it is going to take some time to turn this around.

"There will be incidents, incidents have always happened in prisons."

His concerns about drug-fuelled violence in jails and staffing levels are shared by the former governor of Albany and Wormwood Scrubs prisons, Keith Munns.

He told Sky News: "People are taking things, they don't know how it is going to affect them and it is affecting their behaviour.

"Funding has been cut consecutively and 80%-85% of costs in a prison are staff costs. So if the Government reduces funds each year, the only things than can be reduced really are staff costs, so staff have to go. "

He added: "Prisoners like consistency... very seldom now do prisoners get association time in the evening.

"Very seldom are they out very much during the day, so there is a lot more time when they are locked up and they get frustrated."

Justice Secretary Liz Truss last month unveiled plans for reforms which include putting an extra 2,500 guards in prisons and no-fly zones over jails so that drones cannot drop contraband items.

However, high-profile incidents including the stabbing to death of a prisoner at Pentonville in north London in October and a riot at HMP Bedford have left some believing the service is in crisis and the reforms do not go far enough.

In just one week last month, five dangerous convicts escaped.

Thousands of prison officers also staged a walkout in November over over health and safety fears, amid claims the service is in "meltdown".

Mike Rolfe, chair of the Prison Officers Association, told Sky News: "Birmingham has lost 30 staff in the last few weeks through resignations - people just not wanting to work there any more - it is such a difficult and dangerous job. The whole service is in crisis."

Two wings at HMP Birmingham were badly damaged and two other wings suffered superficial damage. The Ministry of Justice is conducting a "thorough investigation".