What UK band became referred to as "The Only Band That Matters"?

The UK band referred to as "The Only Band That Matters" was The Clash.

The slogan became closely associated with the London punk group during its rise in the late 1970s. It was reportedly coined by Gary Lucas, who worked in CBS Records' creative-services department, and was soon adopted by fans and music journalists. The phrase captured the band's unusually ambitious identity: The Clash presented themselves as more than a conventional punk act, combining political lyrics with reggae, ska, dub, funk, rockabilly and new-wave influences.

The band formed in London in 1976, with Joe Strummer, Mick Jones, Paul Simonon and drummer Nicky "Topper" Headon forming its best-known lineup. Their 1977 debut established them in Britain, while London Calling and Combat Rock broadened their international audience. London Calling in particular became one of rock's most acclaimed albums.

A common mix-up is confusing the slogan with a formal award or official title. It was promotional billing and an adopted epithet, not the band's actual name. The Clash remained active from 1976 to 1986.