A GIANT private firm with expertise in construction will run West Yorkshire’s probation service, under a controversial shake-up.

The contract for monitoring violent criminals has been handed to Interserve, an £850 million multi-national, supported by four charities helping the homeless and drug and alcohol addicts.

The move follows the winding up of the publicly-run probation trust in West Yorkshire – and the 34 others across England – earlier this year.

Chris Grayling, the Justice Secretary, said the changes would “redouble” efforts to bring down reoffending and stop people from becoming victims of crime.

And he dismissed threats of legal action by Napo, the trade union for probation workers, insisting the union “don’t have a basis” for it.But Ian Lawrence, Napo’s general secretary, said there was already “mounting evidence” that the winding up of the probation trusts was damaging supervision of offenders.

He added: “It is purely ideological that Grayling is pressing ahead with his untried and untested so-called reforms to probation.”

And Sadiq Khan, Labour’s justice spokesman, said: “David Cameron’s Government is putting companies with little or no track record in criminal justice in charge of dangerous and violent offenders.”

But Mr Grayling has inserted what has been dubbed a “poison pill” cancelling clause – landing any future Government planning to reverse the changes with a £300m bill.

Under the shake-up, only the 31,000 highest-risk offenders in Britain will now be monitored by a publicly-run probation service, at a national level.

In West Yorkshire, the rest - including more than 12,000 violent criminals – will be supervised by a partnership called ‘Purple Futures’.

It will include the charities Shelter (housing), Addaction (drug and alcohol), P3 (various issues) and 3SC (unemployment and skills).