Volume One of the series (The Invisibles: Say you want a revolution, 1995) features various radical and libertarian references including Timothy Leary, de Sade, Kropotkin, Shelley and the Situationists (a key character is named King Mob - named after the 1960s pro-situationist group who ironically used to detourn Marvel comics with radical slogans), not to mention an implicit debt to William Burroughs.
Then of course there are the mysteries of London, into which a young Invisibles recruit is initiated by a wise homeless beggar. The latter rants 'Two Londons there are: there's the one you can see all around and there's the other city under the skin of this. The hidden city, sunless and silent, if you really want to learn, I'll take you there. I'll show you things to make your hair stand up'. Later underground they visit 'the buried London... the city's dark twin.... reached by secret processional ways; obsolete subway tunnels, the cellars of long-demolished buildings, lost stations and stairways'.