Garda Commissioner Drew Harris has refused an author's request to view Garda security logs of Northern Ireland-registered cars which travelled between Belfast and Classiebawn Castle in Co Sligo, the late Earl Mountbatten's summer home.
Andrew Lownie, author of The Mountbattens: Their Lives And Loves, has told the Belfast Telegraph that Mr Harris, a former senior PSNI officer and liaison with MI5, had declined to disclose the intelligence.
Lownie had wanted access to the files so that he could pursue his inquiries into the alleged trafficking of boys from London and Belfast, especially from Kincora House, to provide sexual services to Lord Mountbatten in the 1970s when on his annual August holiday.
Earlier this year Lownie revealed recently-released FBI files, which alleged it had information that Lord Mountbatten was a paedophile with a taste for young boys.
Last night Lownie told the Belfast Telegraph that he had written to ask for the Garda logs relating to the period 1969-78 to be released.
"I didn't want there to be any suspicion that I was trying to elicit details of a murder investigation, so I was consciously highly specific about the dates I was asking for disclosure and restricted the dates to the end of August 1978, one full year before Lord Mountbatten was murdered," he said.
"For years there have been rumours that someone, somewhere wanted Mountbatten silenced.
"When you add the Belfast Telegraph revelation that it will be another 55 years before the Kincora files are released, you start to wonder who is protecting who."
Last night a spokesperson for the Irish police said: "An Garda Siochana have nothing further to add to the recent response given to Mr Lownie."
Lownie was told of the decision to continue withholding the records by Chief Superintendent Matthew Nyland of Crime Legal Section, based at Garda HQ in Phoenix Park, Dublin.
Classiebawn Castle was the holiday home of Earl Mountbatten and his family between 1969 and the time of his murder at the hands of the IRA in August 1979.
Lownie told the Belfast Telegraph two months ago how he spoke to two boys who had been trafficked to Classiebawn Castle to provide sexual services to Mountbatten - 'Sean' from Kincora House in Belfast and 'Amal', who had been trafficked to Sligo from London via Belfast.
The two boys were driven to Classiebawn House from Kincora in east Belfast by the late Joseph Mains in August 1977. He is believed to have made regular trips there from Kincora.
In 2015 another Kincora resident, Richard Kerr, told the Belfast Telegraph how he became the favourite of Mains, the warden.
Mains told him he had been fond of another boy who had died, and promised to look out for Mr Kerr.
The boy who had died is believed to have drowned some months after being trafficked to Classiebawn Castle.
His name was Stephen Waring, who, like Sean and Amal, was trafficked to Classiebawn in August 1977 from Kincora.
According to Village magazine, Waring died by suicide within a few months of his encounter with Mountbatten.
He had escaped from Kincora to Liverpool where "he was captured and put back on the Belfast-Liverpool Monarch Ferry from which he plunged into the sea of November 1977".
His body was never recovered.
Lownie said last September that he had written to Mr Harris for help in uncovering secret Garda logs of Northern Ireland-registered cars allegedly trafficking young boys from Belfast.
Lownie (below) is now writing to the Irish Government and the Garda Commissioner to narrow down his request for the Garda logs to August 1977.
"There was no murder plot against Lord Mountbatten in 1977, so why all the official secrecy?" he said last night.
So, who wanted Mountbatten "silenced". And why?
The late Deputy First Minister and former IRA chief of staff Martin McGuinness was the man who gave the go-ahead for the attack on Lord Mountbatten and the bomb ambush that killed 18 soldiers at Narrow Water in Warrenpoint later that same day.
McGuinness had purportedly been embarrassed that the rival INLA had killed Airey Neave MP, widely tipped to be Margaret Thatcher's first choice as Northern Ireland Secretary if she won the forthcoming election, which she did, shortly after Neave's death.
McGuinness had promised the British "a long, hot summer" and, until now, that has been widely seen as the prime and sole motive behind Lord Mountbatten's assassination.
Former Army captain and intelligence officer Colin Wallace, who refused to become involved in 'Clockwork Orange', an attempt to smear various senior British politicians, including Sir Harold Wilson in the 1970s, also tried to warn about Kincora several years before the RUC finally intervened.
Last night Wallace said: "This all goes way, way back to some elements of British military intelligence meddling in politics.
"There were widespread suspicions about the true motivation behind the murder of Airey Neave in 1979 and I think the rot really set in with the Wilson plot.
"Why was this all not disclosed to both the Terry Inquiry and the Hart Inquiry, let alone disclosed to members of the British Parliament?
"I'll tell you why.
"The big danger is that this was all an enormous ball of spaghetti. Once one strand started to unravel, the whole thing would have followed.
"The state wanted to block anything embarrassing from leaking out.
"Once they had started, they simply couldn't stop. And that included misleading the Houses of Parliament.
"Whether or not it went further than that should be the subject of a new, fully-sworn public inquiry."