Probation service staff go on strike today from noon, returning to work at noon tomorrow.

Members of Napo, the trade union for Probation and Family Court staff, balloted for strike action in early October and will walk out of offices in England and Wales later.

There was what is described as an overwhelming vote for strike action to make a stand against the Secretary of State’s plans to privatise 70 per cent of the Probation Service.

Ian Lawrence, Napo general secretary, 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."

Last week three Probation Trust chairmen wrote to Chris Grayling to voice their concerns about his plans and the possible risk of harm to the public if they go ahead.

This coincides with 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."

Since Mr Grayling's announcement in May, Napo has spoken strongly against his proposals.

"People who have committed robbery, domestic violence and other violent offences will be supervised by a fragmented private sector whose main interest will be about making profit for shareholders not protecting the public," said Mr Lawrence.

"Due to the nature of offending, the government has had to factor in fluctuations in offending rates. As such, companies will not be rewarded unless they reduce re-offending by more than three per cent.

"However, they won't be penalised if they allow re-offending to increase by three per cent either. We believe that will perversely encourage companies not to invest in expensive rehabilitation programmes; but rather cut staff and offices and allow re-offending to increase to make the most profit, relying purely on the fee for service to make money.

"This untested, untried reform has to be stopped. There has to be a full parliamentary debate about it, there has to be a pilot to test it first and the timescale for any reform has to be reviewed.

"If Grayling is confident that his plans will reduce re-offending why is he afraid to run a pilot first? This isn't about reducing re-offending this is an ideological attack on the public sector to allow privateers into the justice system."

In an Opposition debate in the House of Commons on October 30, a number of MPs from Labour, Plaid Cymru and the Green Party spoke out against Mr Grayling’s plans with Sadiq Khan, Shadow Justice Minister, calling on the Secretary of State to run a pilot scheme before pushing ahead.

The Offender Rehabilitation Bill, due back in the House of Commons for Second Reading on November 11, will also see those supervised to under-12-months custody supervised on licence for the first time.

Mr Lawrence said: "We welcome the opportunity to work with this group of offenders but it has to be thought through properly.

"It's disproportionate to expect someone who receives just one day custody to then be subject to a 12 month licence period.

"It will lead to a higher number of people being recalled to prison at a time when our prison population is already at bursting point; 50,000 new cases in an under resourced service will lead to real problems.

"Give the existing service the money to work with this group in the way they know works best, instead of taking away resources from the most dangerous offenders".