Telephone...

In a statement to the House of Commons, Grayling said an investigation had found 32 instances where conversations between MPs and prisoners were recorded between 2006 and 2012, in addition to a 'small number' of cases over the last few years where a call between the prisoner and their legal representative was taped.

"It is unacceptable and I want to ensure that we have taken every reasonable step to protect the confidentiality of communications between prisoners and their constituency MPs," said Grayling.

HM chief inspector of prisons, Nick Hardwick, has been asked to conduct an independent investigation into the recordings and report by early 2015 on the full facts and make further recommendations.

Grayling said there was 'nothing' to suggest listening in on prisoners' calls was intentional: "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."