In February 1975, the band announced they were splitting with Jonathan King and that they had signed with Mercury Records for US$1 million. The catalyst for the deal was one song – "I'm Not in Love". Stewart recalled:
Speaking in the BBC Four documentary I'm Not In Love: The Story of 10cc in 2015, Stewart explained that the band, three years into a five-year contract with King were earning a mere 4% of royalties. Creme made it clear that the band had fully intended to sign with Richard Branson's fledgling Virgin label, with the band's records to be released in the US through Atlantic. Stewart and Creme were about to go on holiday, however, and had left their manager Harvey Lisberg with power of attorney to accept the Branson offer. No sooner had they left the country, but another higher bid arrived from Phonogram and was accepted by the management team, including Lisberg. Creme said that he felt "horrified, embarrassed and disgusted - to this day I still am".
The Original Soundtrack, which was already complete, was released just weeks later. It was both a critical and commercial success and featured distinctive cover art created by the Hipgnosis team and drawn by musician and artist Humphrey Ocean. It is also notable for its opening track, Godley & Creme's "Une Nuit A Paris (One Night in Paris)", an eight-minute, multi-part "mini-operetta" that is thought to have been an influence on "Bohemian Rhapsody" by Queen.