Barnett and Sheilagh Brown began a closer design association with Quorum, designing both under their own names and the Barnett and Brown eponym.[3] Their joint label continued to gain in momentum after Quorum closed in 1975.[1][4][5] While the label was critically successful, it would later flounder financially. Speaking in 2009 in a film produced for the Super Contemporary exhibition at London's Design Museum, Brown recalled how the duo had set up shop in South Molton Street opposite Browns adding: "We did the clothes that everybody wanted. If they couldn't afford them – they had giant buttons – they would steal the buttons off the clothes. We were in every fashion magazine; we were the feted couple".[3]
By the early 1980s, Barnett had become an established part of what Brenda Polan and Roger Tredre described as London fashion's "creative renaissance", with a peer group that included Vivienne Westwood, Wendy Dagworthy, BodyMap and Katharine Hamnett[6] He won the Dress of the Year award in 1983 – his linen dress and coat was selected by Observer fashion editor Sally Brampton.[7] An article about London Fashion Week in The New York Times in 1984 singled out Barnett – alongside Jean Muir and Zandra Rhodes – as being of world-class calibre, adding: "Sheridan Barnett blends British understatement and a dash of American sportswear in his unobtrusive designs".[8]
Barnett always considered himself a freelance designer and also collaborated with more traditional fashion names, including Jaeger and Norman Hartnell.[1] His collaboration with Hartnell – working alongside the designers Victor Edelstein and Allahn McCrae – was greeted enthusiastically by The New York Times in 1986. "The tailored day clothes by Mr. Barnett are the most impressive, carrying some of the slickness of Italian workmanship in well-made coats and suits."[9] In the 1990s, Barnett worked with Marks & Spencer fashion supplier Claremont.[1]
Alongside his design work, Barnett worked as a tutor at Central Saint Martins, where his students included John Galliano.[1] During his early design career, he also employed Galiano's successor at Christian Dior Bill Gaytten.[10]