Kate Isitt plays Susan’s best friend Sally. A beautician, Sally is terrified of growing old and the effect that gravity can have on her face and bottom. Secretly afraid of being a spinster, Sally is desperate for a man - until she falls head over heels for Patrick, an unapologetic ladies' man and committed Tory.

Steven Moffat comments: "Emotionally ravenous, desperately insecure and very needy, Sally is so aware of her own insecurities and weaknesses that she's inadvertently cruel to the people around her. She assumes nothing will work out for her, so she takes a pessimistic view on all the good things that happen to her. She's very quick to assume she's about to get hurt, and therefore gets upset in advance. In fact, she has a fairly good time throughout the series, but she never actually notices!"

Kate laughs: "I suppose when the series began, Sally was mainly there as Susan's paranoid and needy best friend. She was belligerently single, twisted and desperate. But now all of the relationships have blossomed, and we are seeing more of her independent life. This new romance with Patrick is a big thing to Sally, and it's mutated into something much more for both of them. Now she is living a dream. Patrick really turns her on! He has disgusting self-confidence and is not called tripod man for nothing. He has no morals and very little brain! It's inspired writing, and Steven has written a lovely part for me! Sally and I are very different, but I love working on her vulnerability - on the surface she's cruel, but that's more fun to play than niceness!"

But Kate did have one particularly nerve-wracking moment in the new series - she makes her singing debut - to great comic effect…