US Edition He was a particularly insightful interpreter of Mahler, not least in Deryck Cooke's completed version of the composer's drafted Tenth Symphony, which in 1972 Morris was the first to commit to disc. He did the same in 1988 with Barry Cooper's realisation of the sketches for Beethoven's Tenth Symphony, but with less success.
He conducted for the Investiture of the Prince of Wales in 1969 and, on one startling occasion, persuaded Baroness Thatcher to record Abraham Lincoln's Gettysburg Address to the strains of music by the Left wing American composer Aaron Copland. He later suggested taking the performance on the road, but the lady was not for touring.
Once described as a "Celtic Furtwängler", Morris was an inspirational and at times spontaneous musician. However he never understood the system – that contracts had to be honoured, that colleagues had to be treated with respect and that sometimes discretion is the better part of valour. He was at his worst when he was secure. Offered a post by the London Symphony Orchestra, he issued a writ claiming exploitation; given a contract by a record company, he countered with a rival deal scribbled on the back of a paper napkin during a late-night drinking session.
Yet when the music began, magic filled the air. Orchestral players responded to this wayward maestro as if a bolt of electricity had shot through their ranks. His concerts – particularly in his early days – garnered glowing reviews. So inspiring was he on the podium that numerous investors put their faith and funds into his talent, alas rarely to be repaid in cash.
Morris was at various times director of the Royal National Eisteddfod in Wales, the Royal Choral Society and the Huddersfield Choral Society, but each engagement ended in tears. Latterly he worked with the New Queen's Hall Orchestra, re-founded in 1992 by John Boyden to reproduce the sounds of Henry Wood's original musicians. After four triumphant concerts at the Barbican in 1998 however, he became so abusive to individual players that he had to be "promoted" to the honorary position of principal conductor.
Wyn Morris was born in Trellech, Monmouthshire, on February 14 1929, the son of Haydn Morris, a noted Welsh composer. He was seven before he learnt any English and claimed to have discovered music by listening to wartime performances by Wilhelm Furtwängler on German radio. He studied at the Royal Academy of Music in London and the Mozarteum in Salzburg, where he worked with Igor Markevitch.
His first serious brush with authority came during his National Service (1951-53) when, as a band leader with the Royal Artillery, he introduced an irreverent ditty into The British Grenadiers march during a passing out parade. By this time he had already conducted the Yorkshire Symphony Orchestra at the Festival Hall.
Returning to the land of his origins he founded the Welsh Symphony Orchestra in 1954, but he was soon at Tanglewood, Massachusetts, where his receipt of the Koussevitsky Memorial Prize in 1957 (the first Briton to be so honoured) brought him to the attention of George Szell, then conductor of the mighty Cleveland Orchestra.
Szell, always a harsh taskmaster, took Morris under his wing for three years and instilled in the student a degree of musical rigour. In 1958 Morris was a finalist in a conductors' competition run by the Liverpool Philharmonic.
His biggest break in Britain came in 1963 when he conducted the Royal Philharmonic in Mahler's Ninth Symphony at the Festival Hall.
"Not since the late Bruno Walter have we heard such persuasive and thoroughly idiomatic rendering of this mammoth score," declared one critic. Other notices from this decade offered similar sentiments. Morris was appointed director of the London Chamber Orchestra in 1964, founded the Symphonica of London in 1965 – with whom he made a speciality of performing Mahler – and worked with orchestras such as the London Philharmonic and the Pro Arte.
When Malcolm Sargent died in 1967, Morris took over a number of his engagements, including a memorable performance of Elgar's The Kingdom at the Royal Albert Hall. The following year he was appointed to succeed Sargent at the Royal Choral Society, directing the choir in the first British performance of the choral version of Strauss's The Blue Danube.
However, his reviews were becoming decidedly mixed and his behaviour erratic. In 1970 the Society decided not to extend his two year trial period, criticising him for meddling in administrative matters. The row spilled into the press. Some members of the Society denounced their own committee, while others drew attention to Morris's "unusual training methods... physical and vocal". Eventually Morris and around 70 dissenting members established the Bruckner-Mahler Choir, which soon gave a mesmerising first British performance of Rachmaninov's Vespers.
In the meantime Morris had, in 1969, been appointed to the celebrated Huddersfield Choral Society where he soon became embroiled in a spat with its regular orchestra, the Liverpool Philharmonic, after suggestions that some of its instrumentalists were disrespectful by chewing during a Messiah performance. That appointment ended in acrimony in 1974 after a rendition of Elgar's Dream of Gerontius was described as the longest ever given.
Now he was a virtual pariah, not just a mischievous maestro but a musical liability who was living in a fantasy world; behind his back he was known as "Wind" Morris thanks to his ability to engage in extensive accounts of how he should have been a great success. When, in 1984, a rare opportunity came to conduct the LSO on a Wagner recording, he seized it – only admitting to the producer as the session began that he had not held a baton for nine years. On the basis of that disc the LSO was reportedly poised to offer him a contract. True to form, Morris snatched defeat from the jaws of victory by instructing the lawyer Oscar Beuselinck to issue a series of writs against the band and his advisers.
He fell in with Isabella Wallich, a niece of the recording pioneer Fred Gaisberg. She was devoted to all things Welsh and established the Delyse record label to record Welsh folk music. Her commitment extended to Welsh people and Morris was able to record for her a highly-regarded account of Mahler's Das Knaben Wunderhorn with the young Janet Baker. He also recorded a hugely successful Beethoven cycle for the Pickwick label.
In many ways Wyn Morris belonged to a bygone era. Thomas Beecham had succeeded by establishing new orchestras; in the late 20th century a conductor succeeded by working in established orchestras, with programmes and priorities chosen as much for political as for professional reasons. Where Arturo Toscanini could be a tyrant, Morris had to behave. His tragedy was that, with all his remarkable musical talents, he could not – or would not – conform.
Wyn Morris married, in 1962, Ruth McDowell, with whom he had a son and a daughter. He is survived by Elena Rogers, his companion of the past 30 years.