Fears over public safety have led to a delay in privatising a large part of the probation service, shadow justice secretary Sadiq Khan said yesterday.

Justice Secretary Chris Grayling has announced that all probation trusts have received formal notice that their contracts will end on May 31 - two months later than originally planned.

Mr Khan claimed concerns over public safety are behind the delay and called for the shake-up to be abandoned completely.

The Probation Chiefs Association (PCA) said in a statement that even with a two-month delay the timetable to award £450 million of probation contracts to private and voluntary sector organisations was "extremely pressured."

Those who win contracts will supervise 225,000 low and medium-risk offenders each year on a payment-by-results basis.

Mr Khan said: "We already know through newspaper reports that the Ministry of Justice's own internal risk assessment warned of the very high chance probation privatisation would put public safety at risk.

"If reports I'm hearing are true that today's announcement of a delay is due to fears over public safety, then ministers need to come clean.

"But a two-month delay is still not enough. With no evidence fragmenting supervision of serious and violent offenders and bringing in big multinational companies will do anything to improve reoffending rates while keeping the public safe, the only sensible option is for this whole reckless gamble with public safety to be abandoned."

The PCA said in a statement: "The PCA understands the need for the government to delay the date for terminating probation trust contracts, originally scheduled for March 31 2014. However, it still remains that the timetable for transition is extremely pressured.

"We have concerns that if the transitionary infrastructure is not implemented carefully and fully tested before the new organisations 'go live' on the June 1 2014, this could have serious risks of an unacceptable fall in probation service quality and public safety implications."

A spokesperson for probation officers' union Napo said they are feeling "very positive" that a justice select committee report due to be released on Wednesday and a House of Lords debate next week will further pave the way for Mr Graylings' plans to be disrupted.