THE novelist, playwright and journalist William Watson wrote what he called "serious fictions" under his own name and thrillers pseudonymously as J K Mayo, which one perceptive reviewer described as "Le Carre without the longueurs".

His debut novel, BetterThan One, was published in 1969. Ten years later came Beltran in Exile. Both were well-received but sold unspectacularly. Another serious fiction, Night on the Bridge, made little impact and thereafter Watson - known to his friends as Bill - turned to thrillers, featuring Colonel Harry Seddall, a British secret agent who, according to another reviewer, "is to cynicism what Harry Secombe is to sincerity".

The Seddall novels, including The Hunting Season, Wolf's Head, Cry Havoc, A Shred of Honour and Interloper are taut, elliptical, intricately plotted and frequently violent. It was said that they were the preferred reading of those plotting the downfall of Margaret Thatcher. Be that as it may, Seddall has never entered the popular consciousness like George Smiley or James Bond. For Watson, writing thrillers was "a journey through plot, whereas writing a straight novel is a journey with yourself alone".

He was born in Edinburgh. His fatherwas a well-to-do and exceptionally well-connected lawyer, the deputy keeper of the Signet. Sitting in his office in St Andrew Square, he once told his son: "Watson, I'm the chairman of Scottish Union and National Insurance Company, law agent for the Royal Bank of Scotland and chairman of the British Linen Bank." His mother was the daughter of an Edinburgh deputy chief constable. He attended Edinburgh Academy though he always insisted he would rather have gone to the High School. His father hoped he would follow him into the law but he survived neither the university of Oxford nor Edinburgh because of a "splendid disregard of work".

It was therefore perhaps inevitable he should drift into journalism. His first job was assistant picture editor on the Scotsman, then under the inspirational editorship of Alastair Dunnett. Subsequently Watson became literary and features editor and the first editor of the innovative Weekend Scotsman.

It was a period during which the Scotsman was in the ascendant and Watson was one of several of its stars. Among the staff writers he could call upon were Magnus Magnusson, Gus MacDonald (now Lord MacDonald) and David Kemp.

Playing Sebastian Flyte to Watson's Charles Ryder - or was it the other way round? - was Christopher MacLehose, who later founded the discriminating publisher Collins Harvill. In the old Scotsman building on Edinburgh's North Bridge, the bohemian couple occupied a cubby-hole, permanently engulfed in smoke, where they played chess and kept a record-player going constantly, even when they were not in residence.

Amazingly, despite such eccentric behaviour, some work did get done and Watson is credited with adding the novelist and poet Robert Nye, literary scholar Isobel Murray and the critic Derek Stanford to the roster of the paper's reviewers. He also tried his editor's patience by publishing reviews of books a few tributaries off the mainstream.

Watson, though, was always more interested in writing books than reviewing them. As well as a novelist, he was a noted playwright. With Nye, he co-wrote Sawney Bean, which was the first play to be produced when the Traverse moved to the Grassmarket. Other plays included Footstool for God, set in Rosslyn Chapel, which was premiered at Pitlochry, and The Larch and Dodwell's Last Trump, which were performed at Perth Rep, where Watson was literary adviser for a spell.

At the outset of the nineties, he drifted back into journalism, night sub-editing on The Herald, which allowed him to spend daylight hours in the fictional vineyard.

The name Mayo, he explained, was borrowed from an Irish friend of his family whom he knew in childhood. The Hunting Season, the first of the Seddall novels, he said was written off the top of his head. "I didn't have a plot. I just put a guy in a car running for the Channel Ferry and let it scoot on from there, " he said.

Later novels in the series, however, were evidently more sophisticatedly constructed, if not entirely convincing every reader. Reviewing A Shred of Honour, Douglas Hurd, the former foreign secretary, deemed preposterous the very idea that the British government could lose a consignment of chemical and bacteriological weaponry.

Watson was twice married, first to Bridget Peck. They were divorced in 1965. His second wife was the theatre director, Catherine Robins, by whom he is survived. He died peacefully in an Edinburgh nursing home after a long illness.

William Hugh Charles Watson; Born April 30 , 1931, died December 5, 2005.