Extreme Noise Terror were formed in early 1985 in Ipswich, England, originally consisting of dual vocalists Dean Jones and Phil Vane, guitarist Pete Hurley, bassist Jerry Clay and drummer Darren “Pig Killer” Olley. Prior to ENT, Vane and Hurley had played with Discharge-influenced acts Freestate and Victims of War, whilst Jones had been singing with Raw Noise. Hurley claims that the band name came from an insert for an album by the Dutch band Lärm: "It featured a bandanna-ed hardcore kid with 'Extreme Noise Terror' surrounding him. Those three words summed up exactly what we were aiming at." Aside from Discharge, the band cite as early influences Anti Cimex, Rattus and Antisect, another early proponent of the "one high, one low" vocal approach. ENT signed to the small UK-based indie label Manic Ears after a solitary gig supporting fellow UK punks Chaos UK.
Their first release for the label was a split LP with Chaos UK in 1986, entitled Radioactive Earslaughter. Although there were still musical similarities between the two bands, ENT were already beginning to twist hardcore into what would later become known as "grindcore". ENT have however expressed misgivings about the use of the term:
We were known as hardcore punk. Then it became this 'Britcore' thing that Sounds and NME came up with, with the Electro Hippies, Napalm, Carcass and Bolt Thrower all rolled into one, all playing the same shows and then Napalm Death made the word 'grind' up. But they were always a bit more metal than us and we didn't really know what this word 'grind' meant.
In 1987, ENT came to the attention of John Peel, on the recommendation of fellow Ipswich group The Stupids. After seeing them live at the Caribbean Centre in Ipswich with his wife and son, Peel offered them their first (of four) Peel Session for BBC Radio 1, which was released through Strange Fruit. A second Peel Session was recorded the following May.
During this period, the drum stool was filled by former Napalm Death drummer Mick Harris, although he left soon afterward to form Scorn and was replaced by Tony "Stick" Dickens (of crust band Doom). Bassist Clay was replaced by Mark Gardener, and this line-up recorded ENT's debut album, A Holocaust in Your Head, which was later voted number 3 in Terrorizer's essential European grindcore albums, who described it as "marrying a thick crust-punk crunch and vitriolic lyrical assault with the newborn, clattering fury of grindcore, 'Holocaust...' followed Napalm's heroic uppercuts and haymakers with a Doc Martin in the goolies." The band undertook a headline tour of both Europe and Japan in support of the album. In 1990, Jones and future ENT guitarist Ali Firouzbakht guested on Raw Noise's "Sound of Destruction" single release, and bassist Gardener was replaced by Peter Nash from the band Doom.