Officers have been told to work to rule after delegates at the annual conference of the Prison Officers Association (POA) voted to step up action in their pay dispute with the Government.

The move follows last year's national strike – the first in the POA's 68-year history – which affected Durham, Frankland and Low Newton jails, and custody hearings at North East courts.

It is said the latest action, to include arriving for work at jails at the start of shift rather than early to prepare for work, will have a "serious" effect on the running of prisons by the end of the week.

The Ministry of Justice warned that industrial action would put staff, prisoners and the public at risk, and pointed out that prison officers' pay had been determined by an independent review body.

However, union officials have described the latest 2.2 per cent pay award as an "insult," and criticised the rises which officers have received over the past four years.

POA chairman Colin Moses, from Washington, said: "The employers and the Government have constantly abused the goodwill of staff throughout the UK.

"It is clear that prison regimes cannot be maintained, unless additional resources are put in place, if the employees work the hours that they are paid for."

General secretary Brian Cayton said: "The prison service abuses the policies when it suits their needs, but when something goes wrong they immediately apportion blame to the staff and sack the workers."

As well as pay, prison officers are concerned about safety – assaults on staff are increasing.

There has been a spate of violent incidents involving prisoners at Frankland, at Brasside, which houses more than 700 of Britain's most dangerous convicts.

Last year, the cell of Hussain Osman, one of the failed July 21 suicide bombers, was set on fire, and al-Qaida terrorist Dhiren Barot was injured when boiling liquid was poured over him.

Justice Secretary Jack Straw was due to address the POA conference in Portsmouth today.