Introduced by actor Ian Charleson to director Derek Jarman, Willcox was offered 'any part you want' in Jubilee (called Down with the Queen at the time). Plagued by budgetary issues, the film featured Willcox as the murderous 'Mad', as well as a number of other prominent figures from the punk scene. She went on to play 'Monkey' in the 1979 film of The Who's Quadrophenia, having been introduced to director Franc Roddam through an association with John Lydon. Willcox demanded the part of Monkey from Roddam. She completed filming despite requiring medical attention for pneumonia.
The possibility of a role in the Sex Pistols' film, The Great Rock 'n' Roll Swindle under director Russ Meyer having fallen through, Willcox went on to play Miranda in Derek Jarman's version of The Tempest, which won her a nomination as Best Newcomer at the 1980 Evening Standard Awards. Continuing a stage career alongside film work, in 1979, on London's Royal Court Theatre stage, Willcox played Sharon in Nigel Williams' Sugar and Spice, Tallulah in Stephen Poliakoff's American Days at the ICA, playing alongside Mel Smith, Antony Sher and Phil Daniels and taking a film role opposite Katharine Hepburn in the made-for-television film The Corn Is Green, directed by George Cukor.
In London, Willcox lived in a place called "Mayhem", a converted British Rail warehouse serving as a studio. It was here the band Toyah recorded their first demos. For the lack of proper bed she slept for a while in a "second-hand" coffin, reportedly used by the French Red Cross to transport victims of fatal accidents. Citing her role in Quadrophenia as a boost to her musical career, with growing audiences Toyah signed to Safari Records, releasing a debut single "Victims of the Riddle", which topped the UK Indie Charts. This was followed by the Sheep Farming in Barnet EP, produced by Steve James and Keith Hale. Initially released in Germany, in 1979 it was re-released as an LP, comprising the original six tracks, "Victims of the Riddle" A and B sides and three tracks that were previously unavailable on vinyl. Willcox's second album, The Blue Meaning, went up to no. 40 in the UK Albums Chart in June 1980. By this time she is reported as announcing she had severed all ties with punk aesthetics.