Unison will throw its weight behind the fight against police and probation service privatisation, including balloting members for industrial action.

The union's general secretary Dave Prentis is speaking at the union's Police and Justice Conference in Brighton today where he will vow to battle against murky security corporations.

Mr Prentis said: "Mr Cameron can shuffle his Cabinet anyway he likes, but the result is still the same - a bad deal for the public.

"The jokers in the police pack are the likes of Serco and G4S who are themselves under investigation for potential fraud. Staff at Serco accused of overcharging for transporting prisoners to court, while G4S found guilty of overcharging for electronic tagging."

The situation is so dire, Mr Prentis will tell delegates, that he is demanding a public inquiry into the effects of privatisation.

He said: "Police staff are committed to the jobs they do and are working long and hard to cover the gaps caused by redundancies across the service.

"And you witness daily the ludicrous situation of police officers being used to backfill for police staff posts - taking officers off the front line.

"We need an independent inquiry into privatisation - the companies that provide public services, their employment practices, the quality of services they provide, as well as the profits they make at our expense."

Mr Prentis also had a warning for those intent on decimating the probation service: "I tell you now that Unison will continue to defend the probation service.

"If we have to move to an industrial action ballot in probation to defend our members' interests, Unison's support is there - every step of the way."