Mark Allen, the spy who wrote too much
Were it not for a chance discovery in the aftermath of Libya's civil war, what the world knows of Tony Blair's dealings with Muammar Gaddafi - and the lengths the former British prime minister was prepared to go to find favour - might be a good deal less.
A treasure trove of documents found in 2011 in the offices of the head of Libya's intelligence services detailed British endeavours to cosy up to Gaddafi in the years before his fall - including meetings in the desert between Blair and Gaddafi and the abduction of Libyan dissidents by western intelligence services.
Prominent among the names in these documents was Mark Allen, the head of MI6's head of counter-terrorism unit in 2004, and a correspondent with his Libyan contemporary, Moussa Koussa. The contents of those letters, specifically Allen's, have proved explosive, and continue to reverberate to this day.
I congratulate you on the safe arrival of [Belhaj]... This was the least we could do for you - Sir Mark Allen to Moussa Koussa
Two of the many people "rendered" for Gaddafi were Abdel Hakim Belhaj and his Moroccan wife, Fatima Bouchar. Scooped up by MI6 in Malaysia in 2004, hooded, shackled and delivered to the torture chambers of Gaddafi, Belhaj went on to endure six years of abuse, according to his own account.
The British government on Tuesday lost its appeal to prevent Belhaj's case being heard in court, meaning the spotlight will soon shine on the dark side of Blair's 2004 "deal in the desert" with Gaddafi, and the roles of Allen, the former foreign secretary Jack Straw, and the wider British government.
The documents central to that case show Allen not only taking credit for MI6's work - but insisting on it. In a fax sent by him to Libyan authorities in March 2004, he said that it was Britain, and only Britain, who should take credit and reap the rewards of Belhaj's abduction.
Using an MI6 code name for Belhaj, he said: "I congratulate you on the safe arrival of [Belhaj]. This was the least we could do for you and for Libya to demonstrate the remarkable relationship we have built over recent years.
"Amusingly, we got a request from the Americans to channel requests for information from [Belhaj] through the Americans. I have no intention of doing any such thing. The intelligence about [Belhaj] was British... I feel I have the right to deal with you direct on this”.
Other documents suggested British security and intelligence officers had supplied Belhaj’s interrogators with questions to ask him in prison.
But it is not the only influence Allen appears to have had in the later Gaddafi years. Soon after his correspondence with Koussa, Allen's life branched away from spycraft and into global business.
From MI6 to BP
Allen, a foreign service veteran who had served in Abu Dhabi and Cairo in the 1970s and 80s, abruptly resigned in 2004 as head of counter-terrorism after losing out to John Scarlett to lead MI6.
Knighted for his services to the government in 2005, he was soon installed as a special adviser for BP on Libyan oil contracts, with the approval of the British government.
BP signed a $15bn oil deal with Libya in 2009, with Straw revealing in a leaked letter in the same year that negotiations had included talk of the release of Abdelbaset al-Meghrahi, the Libyan held in a Scottish prison for the bombing of an airliner over the town of Lockerbie in 1988. Megrahi was indeed released soon after the deal was struck.
In 2010, Allen was requested to appear before a US Senate committee over the alleged links between the Lockerbie negotiations and the oil deal. He was blocked by BP from doing so.
But it was a year later, with the fall of Gaddafi, that his fuller role in the Blair-Gaddafi love-in became apparent. Allen and the British government has spent the intervening years fighting to stop any further information coming to court.
British police nevertheless looked into Belhaj's case, amassing 28,000 documents during a "thorough and penetrating" four-year investigation which they passed to the Crown Prosecution Service in 2014.
However, the CPS said there was "insufficient evidence" to bring charges. That decision has been challenged and is the subject of judicial review.
But now all involved on the British side face having the details of their past actions in Libya dredged up in the Belhaj case.
Lawyers say it will be fascinating to see how far the defendants are prepared to pass the buck - whether the abduction of Belhaj and Boucher was the policy of government or whether it was an agent, principally Allen, who had "gone rogue".
Thanks to the Supreme Court ruling on Tuesday, Britain will perhaps eventually have an answer.