[1] It was during his time at school that his singing voice was first observed by the then Physics master, Denis Weatherley, himself a well-known baritone in the county and especially renowned for Northumberland songs.
Allen's initial ambition was to be a doctor but this was later abandoned when he won a place at the Royal College of Music in 1964, where he studied with Hervey Alan for four years, specialising in oratorio and Lieder until 1968.
His early roles with the WNO also included Mozart's Almaviva, Guglielmo and Papageno, Rossini's Figaro, Falke in Die Fledermaus, Billy Budd, Posa, Eugene Onegin and Germont.
Allen also appears in recital in the United Kingdom, throughout Europe, in Australia and America, with his recital repertoire no less extensive than his operatic one; ranging from German Lieder, French songs by Duparc, and English song cycles by Ralph Vaughan Williams to musical numbers by Rodgers and Hammerstein, Jerome Kern and Cole Porter.
He has also recorded oratorio and choral works such as Brahms' Ein deutsches Requiem, Handel's Saul, and Orff's Carmina Burana.
Allen has also been revealed as being the model and inspiration in developing the now famous character of Billy Elliot in the play of the same name by Lee Hall.
[9] In September 2008, he performed under the direction of Woody Allen in Puccini's Gianni Schicchi for the Los Angeles Opera as well as at the Spoleto Festival in June 2009.
During the same year, he took part in the annual BBC Proms, singing songs from numerous MGM musicals such as Gigi, Kismet and On the Town at the Royal Albert Hall, London.
[11] On 27 January 2012, Allen marked his 40th anniversary at the Royal Opera House, Covent Garden, singing the rôle of Don Alfonso in Così fan tutte.
[12] In 2015, he sang the rôle of Baron Zeta in the Metropolitan Opera's production of Franz Lehár's operetta The Merry Widow, which he reprised at the Met in 2017.