She added that the Government was "absolutely committed" to giving prison officers and governors the support they need to do their job and keep them safe.

Announcing the demonstration, which began at midnight, the union said the "continued surge in violence and unprecedented levels of suicide and acts of self-harm", coupled with the recent alleged murder and escapes "demonstrate that the service is in meltdown".

This morning around 60 guards gathered in the car park within the gates of Pentonville Prison, in north London. Dave Todd, POA representative for London, Kent, Surrey and Sussex, said conditions in prisons were "volatile and dangerous".

"We need to act to protect ourselves," he said. "It has not come about quickly - it's a build-up over probably years actually.

"It's just unsafe. To me, prison officers taking this type of action speaks volumes for what's happening inside."

Derek Stanton, a committee member of the Manchester POA, said: "I have been in this job for 28 years, this is the most dangerous I have ever seen it."

Earlier this month two prisoners escaped from Pentonville sparking a manhunt in which they were eventually recaptured.

Weeks earlier, inmate Jamal Mahmoud, 21, died after being stabbed at the jail on October 18 in an attack which left two others injured.