Jon Boutcher

A total of 29 people — 25 senior intelligence experts and four Special Forces crew — died when the helicopter went down on the Mull of Kintyre en route from Northern Ireland to Scotland.

Jon Boutcher has written to the Northern Ireland secretary, Hilary Benn, after meeting with some of the families of the deceased.

In his letter, he urges Mr Benn to “consider exerting any influence you are able upon cabinet colleagues and government officials to enable the families to get answers to the many questions they have”.

A number of families are pursuing a judicial review after calls for a public inquiry were rejected by the UK prime minister, Keir Starmer, and by the Ministry of Defence.

Mr Boutcher’s letter states: “I strongly believe that as Chief Constable of the Police Service of Northern Ireland, I owe a duty of care to both the memory of those fallen officers and to their families.

“Consistent with that duty of care, I intend to lend my voice to their appeal for transparency and openness.

“As you know, 10 of those who died were serving police officers of the Royal Ulster Constabulary GC.

“Even to that resilient organisation, long accustomed to suddenly losing colleagues in violent circumstances, this was a shocking tragedy still remembered today.

“The devastating impact on each family is something that you and I can never truly understand.”

It continues: “The recent decision by the Ministry of Defence (MoD) to seal the files on the crash for 100 years has been particularly difficult for the families to understand.

“I confess to not understanding the justification for such a dramatic position in a democracy where we should champion openness and transparency.

“It is clear to me that a lack of official transparency — whether perceived or actual — is adding to the suffering of these families.

“I have been struck by the many parallels to my work on legacy investigations where secrecy about even uncontroversial material promotes conspiracy theories, distresses families and hinders their ability to achieve any form of closure.”

Separately, the Police Federation for Northern Ireland, the Northern Ireland Retired Police Officers Association, the Intelligence Corps Association, the Superintendents’ Association of Northern Ireland and the Royal Gloucester, Berkshire and Wiltshire and Rifles Association have backed calls for a public inquiry.

In a joint statement, the five organisations appeal to the UK government “to fulfil its promise of a duty of candour, to honour the memory of the fallen, and to heed the call of their families: release the sealed documents and initiate an independent, judge-led public inquiry”.