More than 12,000 violent criminals on probation in West Yorkshire will be handed over to private firms, under explosive plans to be debated today.

The offenders have committed crimes including domestic violence, burglary, robbery, violence against the person and sexual offences, Labour said.

Companies such as G4S and Serco – currently at the centre of fraud inquiries, involving Government contracts – will bid to take over monitoring work.

And the shake-up will see West Yorkshire Probation Trust abolished, despite what it insists is a successful record in cutting re-offending by 14 per cent, since 2005.

The trust has already raised fears that the public will be put at risk if the radical changes to the monitoring of released prisoners go ahead.

Now the warning has been echoed by other trusts across England, which have urged Justice Secretary Chris Grayling to delay the shake-up for at least six months.

Today, Labour will force a Commons debate and reveal the true scale of the change – with 217,569 serious and violent offenders to be handled by private companies.

Of those, 12,219 are on probation in West Yorkshire, the fourth highest figure of any trust area in England and Wales.

They are now categorised as “low and medium risk offenders” – despite having being jailed for serious and violent offences in the past.

Condemning the plans as a “reckless gamble”, Sadiq Khan, Labour’s justice spokesman, said: “We cannot afford to take any risks when public safety is concerned.

“The companies queuing up to profit from the probation sell-off have no track record in delivering these services and some are even under investigation by the Serious Fraud Office.

“It is risky in the extreme to put them in charge of almost 220,000 serious and violent criminals and Labour cannot support such a reckless gamble with public safety.”

But the Ministry of Justice vowed to plough ahead, insisting trials in Peterborough and Doncaster had shown “encouraging falls in reoffending rates”.

A spokesman said: “Almost half those released from prison have returned to crime within 12 months. The public deserves better.

“Our changes will mean, for the first time, every offender leaving prison spends at least 12 months under supervision, where currently around 50,000 are released with no statutory support.”

Under the plans, only the 31,000 highest-risk offenders will be monitored by a publicly-run probation service, at a national level.

Yesterday, the leaders of the Derbyshire, Leicestershire and Warwickshire trusts condemned the plans. One warned of “more preventable serious attacks and deaths”.

Earlier this year, West Yorkshire Probation Trust warned that “fragmentation of offender management will introduce new risks”.

However, yesterday, a spokesman said: “We are unable to comment any further.”