Image copyright bbc Image caption Pat Finucane was shot dead by loyalists in front of his family in 1989

One of David Cameron's closest advisors described the murder of Belfast solicitor Pat Finucane as far worse than anything alleged in Iraq or Afghanistan, the High Court has heard.

Sir Jeremy Heywood also questioned whether the prime minister believed it was right to "renege" on a previous administration's commitment to hold a public inquiry into a killing.

His family are challenging that decision.

Mr Finucane was shot dead in 1989.

On Thursday, Mr Justice Stephens heard how Mr Heywood, now cabinet secretary, referred to Mr Finucane's murder as "a dark moment in the country's history".

Details of emailed correspondence between the top civil servant and another senior Downing Street official were revealed as lawyers for the Finucane family pressed for complete disclosure of notes or recordings from a series of ministerial meetings.

They want the material as part of their legal challenge to the British government's refusal to order a full, independent probe into the 1989 assassination.

A review carried out by lawyer Sir Desmond de Silva QC and published in December confirmed agents of the state were involved in the murder and that it should have been prevented.

Collusion

However, it concluded there had been no overarching state conspiracy in the shooting, carried out by the loyalist Ulster Freedom Fighters at the solicitor's north Belfast home.

Although Mr Cameron expressed shock at the level of collusion uncovered by Sir Desmond, Mr Finuncane's widow, Geraldine claimed it was a sham and a whitewash.

Opening the family's application for discovery of the documents, Barry Macdonald QC said the case was about past and present abuse of state power.

The first instance in 1989 involved the murder of a solicitor perceived to be "a thorn in the side" of the government, police and security services, he claimed.

Mr Macdonald continued: "Secondly, it's about abuse of power in 2011 by the current government when it decided to renege on a solemn commitment to conduct a public inquiry into those events in 1989."

The full scale of what went on has yet to be revealed, according to the barrister.

He told Mr Justice Stephens: "The applicant, Mrs Finucane, knows the name of the person who pulled the trigger. The question is who was pulling the strings?

"In a 500-page report by Sir Desmond de Silva, consideration of the government's role takes up five pages."

Stressing the gravity of the case, Mr Macdonald detailed an email Sir Jeremy sent to Simon King, a private secretary to the prime minister, ahead of a ministerial meeting in July 2011.

In correspondence already disclosed to the parties, he asked: "Does the prime minister seriously think that it's right to renege on a previous government's clear commitment to hold a full judicial inquiry?

"This was a dark moment in the country's history - far worse than anything that was alleged in Iraq/Afghanistan.

"I cannot really think of any argument to defend not having a public inquiry. What am I missing?"

A reply email stated that the prime minister "shares the view this is an awful case, and as bad as it gets, and far worse than any post 9/11 allegation", the court heard.

Transcripts

According to Mr Macdonald, the exchange provided a flavour of the seriousness of the alleged abuse of power in not holding a public inquiry.

Material being sought by the Finuncanes' lawyers includes original notes, minutes, recordings or transcripts of:

A meeting between the Secretary of State for Northern Ireland and Prime Minister on November 5, 2011

A meeting of officials from the Northern Ireland Office, Cabinet Office and Prime Minister's Office on May 16, 2011

A meeting of ministers on July 11, 2011

A Cabinet meeting on October 11, 2011

Copies of letters from MI5 to the Northern Ireland Office in February and March 2011

Paul McLaughlin, appearing for the government, told the court that the decision taken in the Finucane case followed a detailed balancing exercise.

He said it involved weighing any commitment by a previous government against current public interest.

Mr McLaughlin also pointed out that retired Canadian Judge Peter Cory had already examined the case and concluded there should be a public inquiry.

He argued that some of the material being sought would not advance the plaintiff's cause any further.

In a statement, a spokesperson for the prime minister said: "There is nothing we want to add to this story."

Mr Finucane was shot dead by loyalists in front of his wife and children at his north Belfast home in 1989.

Mr Cameron acknowledged in 2011 there had been state collusion in Mr Finucane's murder and apologised to his family.

The hearing continues.