London: Hundreds of confidential telephone calls between prisoners and their MPs may have been recorded and monitored by prison staff, it emerged on Tuesday.

Justice Secretary Chris Grayling was forced to issue an apology and order an investigation after the “serious” breach of privacy was revealed.

He told the Commons that telephone conversations involving at least 32 serving MPs and a small number of lawyers could have been “accidentally” taped by jails.

Prisons routinely record convicts’ calls as part of normal security measures — to ensure an inmate is not, for instance, plotting crimes with a former accomplice or threatening their victims or witnesses.

But communications with constituency MPs about their cases — on issues such as claims of wrongful conviction or appeals — are supposed to be exempt from monitoring.

Grayling said calls may have been eavesdropped between 2006 and 2012, when the Government “tightened up” the system. Ministry of Justice sources said a “few hundred’ conversations had been wrongly tapped. Nick Hardwick, the chief inspector of prisons, has been asked to carry out an independent investigation.

Grayling said the National Offender Management Service had identified details of where calls had mistakenly been recorded. “This is a serious matter and I would like to apologise to the House on behalf of my department,” he said.

“I have as yet seen no evidence that information was passed on to anyone else. I don’t believe this was part of a concerted attempt to monitor, it was simply part of the routine checking of this process to make sure nothing untoward was going on.”