An SAS hit squad staged the death of an IRA suspect to look like an accident as part of a secret operation to avenge Lord Mountbatten's murder, a former Army security expert has claimed.
The Queen's cousin was killed along with his teenage grandson Nicholas Knatchbull and deckhand Paul Maxwell (15) when a bomb was detonated on his fishing boat in Co Sligo on August 27, 1979. The 83-year-old Dowager Lady Brabourne died the following day.
On the same day as the Mountbatten attack, the IRA murdered 18 soldiers in a double-bombing at Narrow Water near Warrenpoint, which marked the biggest loss of military life in a single day during the Troubles.
Graham Yuill told the Mail on Sunday the death of Mountbatten, along with the attack on paratroopers, resulted in the SAS launching missions targeting the Provos responsible for the assassination.
Bomb-maker Thomas McMahon was sentenced to life for Lord Mountbatten's murder but released in 1998 under the terms of the Good Friday Agreement.
Alleged accomplice Francis McGirl had been arrested but was later acquitted. He died in an accident in 1995.
But Mr Yuill claimed he had been informed that McGirl was killed by SAS operatives in retaliation.
"Supposedly he was run over by his own tractor after drinking heavily. I've been told it was made to look that way and the SAS were involved," he said.
"The Provos had killed the Queen's cousin, do you think the British Establishment was going to take that lying down? All bets were off," he added.
His comments come amid claims the late Sinn Fein deputy leader Martin McGuinness was ultimately responsible for Lord Mountbatten's assassination.
Kieran Conway, ex-director of IRA Intelligence, said Mr McGuinness - as Provisional IRA chief of staff at the time - had to "take responsibility".
Sinn Fein has dismissed the claims.
Mr Conway's allegations come in a BBC documentary, The Day Mountbatten Died, to be broadcast this evening to mark the 40th anniversary of the August 27, 1979, attacks.
He claims Mr McGuinness took up the top IRA role a year before the assassination of Mountbatten.
Asked if the attack was ultimately Mr McGuinness's responsibility, Mr Conway replies: "That's right, yeah."
"That's the way it works," he continued.
"If you're the boss, you're the boss, you take responsibility for whatever goes on."
Mr Conway also claims that republican terror chiefs considered killing Lord Mountbatten in the mid-1970s.
Anthony McIntyre, a former Provo who served a prison sentence for murder, also tells tonight's programme that given the target was a close relative of the Queen, he believed it was a decision "taken at the most senior level" of the IRA.
"If they knew about the children, and were quite prepared to go ahead and to sacrifice their lives in order to get Mountbatten, then it's a war crime," he continued.
Mr McGuinness's alleged involvement has been rebuffed by Sinn Fein, with one of its MLAs speaking out in defence of the party's late leader in the Assembly, who died in 2017 aged 66.
Raymond McCartney, ex-terrorist and former IRA H-Blocks commander, said: "It is reprehensible that anyone would make unfounded allegations against a man who is no longer here to defend himself.
"Kieran Conway clearly has no respect for himself or Martin McGuinness and, more importantly, for Martin's wife Bernie and the whole McGuinness family."
The Day Mountbatten Died will be broadcast on BBC One NI and BBC Two at 9pm tonight.