In 2004, she joined the cast of the crime drama, "Silent Witness". As of 2020, she is still in the show and has now played the role of Nikki Alexander for sixteen years. Also in 2004, she played Lady Margaret in Part 2 of "Gunpowder, Treason and Plot", the mini-series about James I (James VI in Scotland) and the Gunpowder Plot. In 2005, Fox appeared in the BBC miniseries The Virgin Queen, a four-part miniseries based upon the life of Queen Elizabeth I,Fox played Amy Dudley, the first wife of Robert Dudley, played by Tom Hardy, despite appearing in only one episode, her character remains a key character in the series. In 2008 she played Sister Jean in Baillie Walsh's "Flashbacks of a Fool", which also featured Daniel Craig. She also starred in "Things To Do Before You're 30" with Billie Piper, who would later marry her first cousin Laurence Fox, although in 2016 they divorced.