Significant new evidence has been uncovered by an English police chief investigating more than 50 murders linked to the British Army's notorious IRA agent Stakeknife.

Victims' families have told stories never divulged before at the start of an independent probe by Bedfordshire Police Chief Constable Jon Boutcher into the high-ranking mole who led the IRA's internal security unit, 'nutting squad', while in the employ of the British state.

A group of six international policing experts has been appointed to inform the investigation on a voluntary basis.

They include senior police officers from the US, Scotland, an Australian ex-officer and ex-Northern Ireland police ombudsman Nuala O'Loan.

In 2003, Stakeknife was widely named as west Belfast man Freddie Scappaticci but he has always strongly denied the allegation.

Mr Boutcher said: "This week we have heard things that, from what the families have told me, they have never told anyone before, because nobody has asked them.

"What I have been told this week is significant evidence against the people responsible for these offences."

He has asked the victims' families to give him time to investigate and recover the evidence.

"It is incredible what I have heard.

"There is a pessimism which I understand, I completely get, because people felt let down and almost abandoned.

"It almost feels like their rights were taken away from them because of the nature of what happened to their loved ones.

"They have now got a voice and that is this investigation, and they told me of what they saw at that time that they have never been able to tell anybody before and we need people to do that," added Mr Boutcher.