"Spies" was conceived by Williams as a nostalgic mid-tempo guitar track, described as "a hymn to nostalgia" for its melodic writing and references to the atmosphere of the Britpop era.
HotPress described "Spies" as an "uplifting" and "guitar-driven" single, noting its melodic chorus and its role in framing the sound of the upcoming album. In Sweden, the news service Omni summarised press commentary by noting that Williams was embracing a "rawer, hymn-like" approach that aligned with the album's Britpop theme.