We are not going to be frightened and intimidated by a management that doesn't take seriously the risks

Duncan Keys Prison Service

But the Prison Officers Association (POA) remains adamant that the scheme is unfair and it is threatening not to co-operate.

Every prison officer in England and Wales takes an average of 14 sick days a year.

Negotiations on a new formula for sick leave have been continuing slowly but in the absence of full agreement, the service will impose new arrangements from Tuesday.

The new system, imposed as a "prison service order", could trigger disciplinary action or even dismissal if staff exceed agreed levels of sickness.

Scotland trial

The "Bradford Formula" works by multiplying the frequency of periods of absence by the total number of days absent.

A similar scheme in Scotland has reportedly cut staff absence by 20%.

But a spokesman for the POA said prison officers suffered violence during work which was anti-social and caused great stress.

The service is no longer prepared to tolerate excessive and unwarranted staff sickness absence

Martin Narey Prison Service director general

The union has lodged a formal complaint and plans to taken the matter to the conciliation service Acas.

POA spokesman Duncan Keys said: "We believe our members who are ill need to be properly protected and not pressurised into returning to work for fear of being sacked.

"This system, which is being imposed on them, is totally unfair when you bear in mind that they have the most stressful job in the UK.

"Every day of every week of every month, seven prison officers are assaulted - I think that puts the 14 days' sick figure in some context.

"Our officers look after 65,000 people who don't want to be in prison, who are anti-social, violent, unpredictable and who, in many cases, are mentally ill and would think nothing of assaulting a prison officer."

Financial cost

Martin Narey, director general of the Prison Service, said something had to be done to address current sickness levels.

Mr Narey said: "The financial cost alone of this is over �65 million a year. This is grossly unacceptable.

"This places a huge strain on prisons and their staff and can stand in the way of providing prisoners with decent and constructive regimes.

"The introduction of the new guidelines, incorporating the Bradford Formula, sends a clear message that the service is no longer prepared to tolerate excessive and unwarranted staff sickness absence."

Mr Keys added: "We hope we will be able to discuss this matter with Mr Narey and reach a sensible conclusion.

"We are not going to let our members be frightened and intimidated by a management that doesn't take seriously the risks they work under."