in the Sky, and Broken News. She played the leading part of DI Susan Taylor in the ITV thriller serial Touching Evil in 1997, co-starring opposite Robson Green. She also appeared in its two sequel serials in 1998 and 1999. Also in 1999, she took the lead role in the post-apocalyptic drama serial The Last Train, also screened on ITV (and written by future Spooks writer Matthew Graham). Also in 2003, Walker played Molly Millions in the BBC Radio adaptation of Neuromancer by William Gibson. In 2003, with the production team of Kudos Television looking to replace the character played by Jenny Agutter in Series 1 of Spooks, the part of Ruth Evershed was specially written for Walker from Series 2. She remained with the show until the fifth series, during the production of which it was announced she was expecting her first child and would be leaving. She returned in 2009 and continued until the series ended in 2011. Benji Wilson of The Daily Telegraph praised Walker's performance, stating: "an actress who has squeezed every drop out of TV’s greatest ever largely dumbstruck doormat for the best part of a decade. Her scenes with Peter Firth, another fine player, have become self-contained little bubbles of weltschmerz within every recent episode". In 2007, Walker had a prominent supporting role as a child snatcher in the ITV1 drama serial Torn and appeared in the BBC adaptation of Oliver Twist. In 2009, she appeared as a maid in a new BBC adaptation of Henry James' The Turn of the Screw, which also starred Michelle Dockery and Sue Johnston. In 2010, Walker appeared as a beleaguered wife (Linda Shand) of a murderer in an episode of the BBC1 crime thriller Luther. In February 2011, she appeared as nervous social worker Wendy in the BBC TV series Being Human. In February 2012, she played a major character in the one off BBC crime drama Inside Men. From 2012 to 2020, she appeared as Gillian Greenwood (née Buttershaw) alongside Derek Jacobi, Anne Reid and Sarah Lancashire in five series of the BBC original drama Last Tango in Halifax. Walker was twice nominated (2014, 2017) for a Television BAFTA for Best Supporting Actress for this role. In February and March 2013, Walker reunited with her former Cambridge Footlights colleague Sue Perkins in the BBC comedy Heading Out. She then appeared in the second series of Prisoners'