Their next single release was " Your Mother's Got a Penis", with an accompanying video based on a supermarket theme. However, this version of the album was missing two tracks – "Maggot" and "You Knows I Loves You". The album was released in May 2005 in the US with the title Straight Outta Newport, with cover art similar to N.W.A's album Straight Outta Compton. It was released in September 2004, and debuted at number 5 in the UK Albums Chart. Their first nationally released album was called Greatest Hits, the name a play on both the group's previous lack of commercial success and their "stoner" image it compiled a mixture of new material and selections from their previous six unofficial albums. The B-side was the album track " Soapbar". With the tagline "The gun is the tool, the mind is the weapon", the track became a popular radio hit, satirising the American hip hop scene. In August 2004, the group reached number 3 in the UK Singles Chart with "Guns Don't Kill People, Rappers Do". The song namechecks many well-known 1980s 8-bit computer systems including Binatone, ZX Spectrum, Commodore 64, ZX81 and BBC Micro. " Half Man Half Machine" was a surreal song about Eggsy believing he was a robot, dressing up in foil, and going to the shops to buy cigarettes and crisps. When group member Rhys Hutchings was phoned by BBC chart presenter Wes on the Official Chart Show to be informed of this, Xain informed the rest of the band that they had reached number 1, much to the shock of the DJ. GLC's first UK chart entry was " Half Man Half Machine", which reached the Top 40 in the UK Singles Chart. The group form part of an era known as Cool Cymru for the popularity of Welsh music and arts internationally in that period. GLC went on to support The Darkness in the latter stages of their UK tour.
The band came to the attention of label executive Korda Marshall, who heard the group's music played by members of The Darkness whilst on tour. They signed to East West Records, the home of rock band The Darkness. The group recorded six albums prior to securing a major record deal. 3 Sponsorship of Newport County Football Club.