With the obvious exception of this final, tragic episode (the truth of which remains unknown), Costello used controversy throughout his life to draw attention to himself and his causes. I was a happy co- conspirator in the early days when we burnt pictures of the Rolling Stones on the floor of the Cambridge Union in 1965 as a stunt that earned suitable splash coverage in the tabloids.
But publicity for Costello became more than mere youthful exhibitionism. It was one of the weapons he deployed in the battle of his life, as an espionage historian, against the academic and intelligence establishments of Britain and America.
His Cambridge career anticipated many of the patterns of his later life. He was the outsider who challenged the establishment: no varnished old Etonian, he proudly boasted that he had attended a comprehensive school. He went to Fitzwilliam House rather than a polished college such as Trinity or King's, yet he managed to be elected by the sheer power of his personality as Secretary of the Union, Chairman of the Cambridge University Conservative Association; he was one of the founders of Pest (Pressure for Economic and Social Toryism) and one of the joint founders of Tory, a one-off magazine that I helped him start in Oxford and Cambridge. Had he followed this trail further, Costello might have ended up in the Cabinet. But, ever the outsider, he was dismissive of what he saw as the cardboard cut-outs carving predictable futures for themselves.
Costello drifted for a few years after Cambridge: advertising, television, publishing; none quite gave him the focus and drive of his Cambridge years. He also found it hard to knuckle under in any environment in which he was not the shining star. And so began his evolution into the ''outsider'' historian, working for himself, finding in the end an area of modern history to quarry that the conventional historians had largely failed to unearth.
He began tamely enough with jointly authored books on Concorde (1971) and naval histories on topics such as Jutland (1976) and The Battle of the Atlantic (1977). This was his historian's apprenticeship, for he had eschewed the traditional training ground of post-degree research and the professional protection of being a member of the ''historian's club of Great Britain''. Instead Costello learnt to apply colourful writing to the dry domain of academic history. With The Pacific War (1981), and I Was There: Pearl Harbor (1985) he developed his investigative skills into the area of archive research, discovering previously unknown documents on the one hand and tracking down individual witnesses to give fresh perspectives on the other. Combined with the colourful writing that reflected the ebullience of its author, these books brought Costello reasonable commercial and professional success. Fourteen years on, The Pacific War remains a standard teaching text in American universities. And the impact of his jointly authored Pearl Harbor book earned Costello a regular invitation to lecture at the US Naval Academy at Annapolis.
It was in writing these books that Costello began his extensive study of intelligence history that was the basis of his long-term reputation. His Mask of Treachery (1989) revealed important new material on Anthony Blunt's espionage for the Soviet Union. Ten Days That Saved The West (1991) discovered controversial new evidence suggesting that Rudolf Hess was lured to Britain by MI5. And for Deadly Illusions (1994) he was granted access, for the first time for a Western historian, to the KGB archives in Moscow in a study of the Russian master-spy Alexander Orlov, the eminence grise behind the Oxford and Cambridge spy ring.
None of these later books were welcomed by the intelligence establishment on either side of the Atlantic. It was particularly galling to them that Costello had found a loophole that enabled him to access intelligence documents still classified in Britain that he discovered were available in the US National Archives under the Freedom of Information Act.
It was here that his combative publicity skills, developed in his Cambridge days, reasserted themselves in his working life (they had never been particularly absent in his private life). Without the conventional research support that contemporary historians rely on, he not only uncovered important new materials in the archives but also tracked down and interviewed many of the people concerned within them.
The secretive Intelligence community swiftly closed their doors to this outsider. They wanted no further exposure of the extent of their espionage failures. Nor did Costello get any support from ''professional'' historians jealous that an ''airport historian'' had discovered new information that their own shuffling of old documents had failed to reveal. In particular, his talent for spotting embarrassing documents in the archives were not welcomed within the intelligence establishment.
Only in the United States, where his combative, high- profile style was more of a cultural norm (and where he lived for the past 20 years), did his reputation start to overcome the hostility that his abrasive professional approach generated. This was the price he paid for unleashing the power of sunshine on the pockets of infection his research had revealed. He was determined to get to the bottom of the lies.
As a historian, he took risks as he used instinct and imagination to buttress his scholarship as he had single-handedly to assess a vast array of documentation to put together the jigsaw puzzle of Soviet penetration of Western intelligence.
No historian is right on every point and John Costello was undoubtedly wrong on some details. But it is remarkable how many of his controversial judgements have stood the test of time. And it explains why, particularly in the United States, the intelligence community began to give him credit for his insights into the world of Soviet espionage.
He brought to his private life the same exuberance and passion that characterised his professional life. He was generous to a fault, always bearing uncalled for presents to whatever home he was visiting. Children naturally adopted him as ''magic uncle''. His irreverence and colour gave him a natural ability to play the child while still remaining a powerful and protective adult.
John Edmond Costello, historian: born Newbury, Berkshire 3 May 1943; died 26 August 1995.