In mid-2006, the group returned to the studio to record two new tracks for their first greatest hits collection, titled "". The lead single from the compilation, "Easy" peaked at number 8 on the UK Singles Chart, whilst the compilation album, released in November 2006, peaked at number 3. The album, certified platinum by the BPI, has sold 598,000 copies. In March 2007, the Sugababes collaborated with fellow British girl group Girls Aloud for their eighteenth single, a cover of the song "Walk This Way" by Aerosmith. The track was released as the official single for "Comic Relief". "Walk This Way" became the group's fifth UK number one single.