John Kane, a former senior radio operator at the government communications centre GCHQ, was twice stopped from publishing books revealing what he said were misdemeanours and laxity going on behind its closed doors, but even before High Court injunctions silenced him, two events overtook Britain's intelligence establishment that suggested his assertions were all too likely to be true. The events were a secrets trial in which two journalists were let off with conditional discharges, and the chance discovery of a KGB spy who had worked inside GCHQ and then left, still undetected.
Kane, known to colleagues as "Jock", was a vigorous Scots-born former RAF special operations serviceman whom GCHQ had recruited immediately after the Second World War. He was surprised that his superiors, after he approached them, appeared to take no action to curb what, as a supervisor there, he saw as carelessness and dishonesty all about him.
The most recent revelations from the American whistleblower Edward Snowden concern alleged British wrongdoing in Berlin, but 40 years before that Kane was concerned about nefarious activities abroad. As far back as 1973 Kane held a "muster" at his posting of Little Sai Wan, Hong Kong, to discover what had happened to more than 200 missing documents. He frowned at what appeared to be widespread fiddling of expenses, episodes of drunkenness and failure to keep watch on Chinese cleaners who could pass discarded items on to unfriendly agents. GCHQ staff members' behaviour, he believed, made them vulnerable to blackmail by hostile powers. Eventually he took his worries to MPs and later government ministers, but still, it appeared to him, nothing was done.
He finally began to write an account of what he had seen, detailing in particular the culture at Little Sai Wan. His 32-year career also included postings at Hawklaw near Cupar in Fife, as well as Istanbul, Aden, Singapore, and Belfast.
Information that had come from his campaign for change was used in court in Britain in 1980 by the defence in the "ABC" prosecution at the Old Bailey of the journalists Crispin Aubrey and Duncan Campbell and the former Crown servant John Berry. The journalists received conditional discharges and Berry a six-month suspended sentence after a retrial held because the jury were revealed to have been vetted, and after the judge, Mr Justice Mars-Jones, said he considered the charges had been oppressive.
Granada Television's World in Action followed up Kane's allegations by sending its reporter, the future film director Paul Greengrass, to Hong Kong, where, the programme alleged, a local hotel was found to have a brothel that corruptly obtained its business from visiting GCHQ employees.
GCHQ was said to have told the Foreign Office that Kane's complaints had been addressed, and "action taken where necessary", but critics called the establishment "an unaccountable state within a state." Then in 1982, when Geoffrey Prime, a former GCHQ employee at Cheltenham, revealed that for years he had been passing secrets to the KGB, commentators again remembered Kane's warnings.
Prime had been arrested in connection with sexual offences against young girls, and his unmasking as a spy came only by chance, because he confessed to his wife. He was sentenced to three years' imprisonment for the sexual offences and 35 years for betraying secrets. He was released in 2009.
By this time Kane had retired and settled in Barton on Sea, Hampshire, where, still brooding on his apparently fruitless campaign, he completed a book. This was nearing publication by the London house, Robert Hale, when on a quiet Sunday morning officers from Special Branch knocked on his door, interviewed him, and confiscated the manuscript. Entitled GCHQ: The Negative Asset, it focused on Little Sai Wan. Undaunted, he wrote a second book, The Hidden Depths of Treachery, but when in 1987 this was due to be brought out by Transworld Publishers, now part of Random House, it, too, was stopped by an injunction. Yet no prosecution was ever brought, and Kane attributed the attitudes of those in power to embarrassment.
His campaign prompted questions in Parliament including one from George Foulkes, then MP for Carrick, Cumnock and Doon Valley, on July 25 1985, as to whether criminal proceedings against Kane would be launched. The Attorney General, Sir Michael Havers, replied in a written answer that no decision had yet been taken. On 25 February 1993 the Foreign Secretary, Douglas Hurd, told Rupert Allason, MP for Torbay, in the House of Commons that he had no plans to apply for the lifting of the injunctions against Kane, and that the government's legal costs for obtaining them in the High Court had amounted to £5,870, with another £839 for action taken in the Scottish courts.
Kane appeared in television discussions such as Channel 4's late-night programme After Dark, shown in 1988, and is mentioned in books about the British secret services, but to the end of his life he felt his efforts, which he saw as his duty, had been frustrated.
His service to his country had begun when he joined up on the outbreak of the Second World War. The boy from Coatbridge, Lanarkshire, who was brought up by his father with the help of aunts and other relatives after his mother died when he was two, and who was educated at St Patrick's High School in the town, chose the RAF.
He trained as a radio operator at Blackpool, before going out on dangerous flights over the Atlantic from a base in Cornwall in order to calibrate radar signals. After serving in North Africa and Italy he was sent in 1944 into occupied Yugoslavia, followed by Greece, where he had a close shave in the midst of an erupting left-versus-right civil war. He was given provisional orders to destroy his wireless and encryption machines as fighters surrounded Athens airport, and with his equipment was only just rescued in time.
While in Greece he fell in love with a Greek resistance member, Alexandra, who had been imprisoned for a year in 1941-42 during the German occupation for assisting the evacuation by submarine of stranded troops who had taken part in Britain's thwarted 1941 attempt to help the Greeks hold back the Nazi invaders. The couple kept in touch by letter, and married in London in 1949.
They were to have two sons, Donald and Stuart, and together travelled the world on Kane's three-year GCHQ postings, before divorce parted them in the early 1980s; Alexandra died in 1999. Kane married his second wife, Cynthia, who survives him, in 1983, and in retirement worked as a milkman and school bus driver.
John Kane, senior radio operator and campaigner: born Coatbridge, Lanarkshire 7 April 1921; married 1949 Alexandra (marriage dissolved, died 1999; two sons), 1983 Cynthia; died Bournemouth 27 September 2013.