Media playback is unsupported on your device Media caption Frances Meehan, whose brother Michael Donnelly was shot dead with a plastic bullet in 1981, says the families did not believe the HET could continue investigating their relatives' deaths.

The body set up to probe deaths during the Troubles in Northern Ireland investigated cases where the state was involved with "less rigour" than others, a police watchdog has found.

HM Inspectorate of Constabulary said it appeared the Historical Enquiries Team's (HET) policy was based on a "misrepresentation of the law".

It said their approach was inconsistent and had serious shortcomings.

HET was set up in 2005 to re-examine 3,260 murders.

The report also considered the HET's approach to cases involving the state was inconsistent with the European Convention on Human Rights.

When asked if HET had acted outside of the law, Her Majesty's inspector of constabulary, Stephen Otter said: "We think it was acting unlawfully in regard to state cases because it treats them differently in policy terms and in the way that then acts out in practice.

"So state cases were less effective as a result and effectiveness is a key test of whether it's Article 2 compliant."

HMIC said the Historical Enquiries Team risked undermining the confidence of the families of those who died during the Troubles in its effectiveness and impartiality.

Northern Ireland's chief constable Matt Baggott agreed to a policing board request to commission the review by the HMIC after criticism of HET in a University of Ulster report.

The report, by Dr Patricia Lundy, claimed the HET gave former soldiers preferential treatment and did not properly investigate deaths caused by the military.

The HET rejected the claims in her report.

Responding to the HMIC report, Dr Lundy said: "I think the HET as an organisation itself is irretrievable at this point.

"I think it has implications for lots of different cases, not just the army cases, because we've heard the structural problems, there's no oversight, there's no complaints procedure and really it seemed to me that it was a bit of a law unto itself."

Media playback is unsupported on your device Media caption BBC News' Chris Buckler questions Matt Baggott over HET review.

Mr Otter said Dr Lundy had presented a report that at the time was made out to be untrue.

"I do think she deserves an apology from the chief constable on behalf of the Police Service of Northern Ireland (PSNI)," he said.

"What is indefensible is that she did make these findings in 2009, so for four years nothing was being done to address those findings and I do find that that is very difficult to believe."

Chief Constable Matt Baggott said that all military cases investigated by HET will now be re-examined, and he accepted that "HET put in place a policy that was wrong".

"A differential approach to military cases is wrong and I assure you this has ended," he said.

He also accepted the recommendations of the HMIC report in full and would work to implement them.

The HET is reviewing more than 150 killings by soldiers between 1970 and September 1973.

The HMIC inspection focused on whether the HET's approach to reviewing military cases conformed to current policing standards and policy.

Review

It examined material relating to 31 cases that the HET had reviewed.

HMIC Key findings HET treats cases involving military differently as a matter of policy HET not conforming to current policing standards in a significant number of important areas A lack of explicit systems and processes Different teams adopting different working practices No clearly defined complaints process No independent review of the HET's processes (until now)

HMIC examined if the HET adopted a consistent approach to both military and paramilitary cases.

It also considered if the HET's review process met requirements to ensure it was compliant with human rights legislation.

The report found the HET treats cases involving military differently as a matter of policy and this appeared to be based on a misinterpretation of the law.

It also found that the HET did not always seek verification where a potential interviewee in a state involvement case claimed to be unfit for interview due to illness.

HMIC said this was "entirely wrong" and had led to military cases being reviewed with "less rigour" in some areas than cases not involving military.

The inspection found that none of the 39 cases referred back to the PSNI for investigation since 2010 had involved state involvement.

"It is striking that not one state involvement case relating to the British Army has to date been referred to the PSNI for further investigation or prosecution," the report said.

'Recommendations'

Mr Otter said: "HMIC is concerned that the inconsistencies we found in our review may seriously undermine the capability of the HET's processes to determine whether the force used in killings during the Troubles was justified in state involvement cases, therefore potentially preventing the identification and punishment of those responsible.

"Our recommendations set out fundamental improvements that the PSNI and the HET need to make in order to ensure the team is effective in delivering its objectives in a way that is consistent with the requirements of Article 2 of the European Convention on Human Rights; and commands the confidence of the public of Northern Ireland, and in particular, of the families of the victims of the Troubles."

Media playback is unsupported on your device Media caption HMIC's Stephen Otter, speaks to Vincent Kearney about the report

Mr Otter said the HET was created and continued to operate within an "extraordinary complex social and political context" which presented those who established it with challenges "unparalleled in UK terms".

"This context makes it even more important for the HET to operate to the highest standards of effectiveness and impartiality, so that the people of Northern Ireland, and the families of the victims whose cases are being reviewed, can have confidence in it," he added.

HMIC interviewed more than 180 people from a range of organisations, including HET, criminal justice agencies, and non-governmental bodies.

It also spoke to the families of 13 of the victims, some in Belfast and others in Londonderry.

HMIC said although many people it had spoken to would have preferred the HET to be independent from the PSNI, they also expressed an "almost universal desire" for it to be retained so long as improvements were made to the way it operates.

The HET is a special investigative unit attached to the PSNI to re-examine the deaths of thousands of people in Northern Ireland between 1968 and 1998.

It is an independent unit which is directly accountable to Northern Ireland's chief constable.