[5][6] Additionally, she appeared in the documentary series Great Canal Journeys (2014–2021), travelling on narrowboats with her husband and fellow actor Timothy West.

Scales was born in Sutton Abinger, Surrey, the daughter of John Richardson Illingworth, a cotton salesman who served as a lieutenant with the Wiltshire Regiment in the First World War,[7] and with the Auxiliary Military Pioneer Corps in the Second World War,[8][9] and Catherine, née Scales, known as "Bim", an actress who had for a time attended the Royal Academy of Dramatic Arts and was later with the Liverpool Playhouse's Repertory Company.

[10][11][12][13] Scales had a younger brother, Timothy "Timmo" Illingworth (1934–2017), who became a lieutenant colonel in the Royal Irish Rangers and was appointed an OBE.

Her early work included the (now believed to be lost) second UK adaptation of Pride and Prejudice (1952), Laxdale Hall (1953), Hobson's Choice (1954), The Matchmaker on Broadway (1955), Room at the Top (1959) and Waltz of the Toreadors (1962).

For 10 years,[19] Scales appeared as "Dotty" Turnbull, together with Jane Horrocks as her character's daughter, Kate Neall, in advertisements for UK supermarket chain Tesco.

Scales appeared in a one-woman show called An Evening with Queen Victoria, which also featured the tenor Ian Partridge singing songs written by Prince Albert.

On 16 November 2007, Scales appeared in Children in Need, reprising her role as Sybil Fawlty, the new manager who wants to take over Hotel Babylon.

John Cleese said in an interview on 8 May 2009 that the role of Sybil Fawlty was originally offered to Bridget Turner, who turned down the part, claiming "it wasn't right for her".

[citation needed] Scales appeared in the audio play The Youth of Old Age, produced in 2008 by the Wireless Theatre Company, and available to download free of charge on their website.

However, Ben Bradley, writing for The New York Times Arts & Beats, stated that Scales was the most memorable thing about the show, "[playing] a rich, Miss Havisham-like eccentric, who trails through her house in evening gowns".

[26] Scales starred in the 2011 British live-action 3D family comedy film Horrid Henry: The Movie as the titular character's Great Aunt Greta.

Alongside her husband, Scales appeared in Great Canal Journeys for Channel 4 from 2014 for 10 series, before her deteriorating health brought her television career to an end.

[30] Reviewing Scales's and West's last episode in October 2019 for The Guardian, Jack Seale wrote "Since the first instalment in 2014, the series has charted the long, slow goodbye that is living with dementia, cherishing every moment of precious normality and celebrating how an immersion in nature is the surest way to bring the old Pru back.

[39] Interviewed for the BBC in 2023, soon after celebrating their diamond wedding anniversary, West said, with reference to Scales's dementia: "Somehow we have coped with it and Pru doesn't really think about it.