In 1998, Clarke was approached by a media company representing one of the three companies that operated parts of the London Underground, who were looking for a replacement automated customer announcer. After 18 months of focus-group testing, in which her voice was dubbed
"Marilyn", she was awarded a contract to produce announcements in 1999. Between 2009 and 2017 her voice was replaced on the Circle, District, Hammersmith & City and Victoria lines by announcements voiced by Sarah Parnell; with her voice on the Central Line being replaced by Adrian Hieatt due to the refurbishments. Her other clients include the
BBC,
Gillette,
Virgin,
Classic FM,
Homebase and
Three UK. Along with her solo work, she is the managing director of Just Add Voice, a company which provides voice-over tracks. ==Personal life==