Probation workers in Trowbridge went on strike this week over plans to privatise 70 per cent of the service.

Wiltshire Probation Service staff walked out for 24 hours at noon on Tuesday as part of national action against the plans of Chris Grayling, Secretary of State for Justice.

It is only the fourth Napo (National Association of Probation Officers) strike in the service’s 106-year history.

Napo believes fragmenting a coherent public sector service into 21 private companies will put public protection at risk.

Probation officer Sharon Treasure, 43, was among about 15 workers picketing outside the Trowbridge office. She said: “Striking is not something we take lightly but we’ve gone out because we want to support the service remaining in the public sector.

"The service at the moment is working very well so why change it? The fear is, can they guarantee change will be good?

“We had a lot of support from the public, people tooting their horns and interested in what we were saying.”

Offices in Swindon, Chippenham and Salisbury were also affected.

Ian Lawrence, general secretary for the union, said: "These are unprecedented times for our members as they fight to save the 106-year-old Probation Service.

"They strongly believe, along with other criminal justice agencies and experts that Chris Grayling’s plans will undermine public protection and put communities at risk whilst also not providing the adequate service offenders need to turn their lives around.”

The Probation Trust said it had growing concerns about the two main companies likely to bid for the service, Serco and G4S.

Mr Lawrence said: "It is wholly unacceptable that these two companies are allowed to bid for the Probation Service whilst still under investigation for fraud regarding tagging and given their recent track records with the Olympics, private prisons and prison transport.

“The Probation Service is possibly the best performing public service we have, meeting and exceeding all government targets, reducing re-offending and being awarded the British Gold Award for Excellence in 2011."

Justice minister Jeremy Wright said: “This is a strike in favour of the status quo, which is high reoffending rates and no support for 50,000 short sentenced offenders each year who are currently released without any supervision and go on to commit so much crime in our communities.”