"In this episode, we see a photo of Susan Lynch's character Liz Baildon as a 21-year-old police probationer in a file Cassie looks at for the Hendon Police Academy," Wilson revealed.
"The photo I used is a publicity still of Susan as the villain Tina from a Cracker episode (To Say I Love You) she starred in and which I directed in 1993. I liked having both of Susan’s characters in the show somehow. I hadn’t worked with her in all the years between."
The Jimmy McGovern series starred Robbie Coltrane as hard-drinking criminal psychologist (or "cracker") Fitz and a young Christopher Eccleston as DCI David Bilborough.
The Easter egg is a nice way to honour Cracker, but could it also hide a deeper meaning? Considering Lynch was the villain in the classic crime series, could she also be the one responsible for Walsh's death in Unforgotten?
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The new series of Unforgotten is quickly becoming the show's most successful to date, with the first episode garnering 7.4 million views, becoming its most-watched episode ever.