Daughter of Edward Lay and his wife Margaret (née Hewitt).
Educated (1944-1947) at St. Dominic's Convent, Harrow-on-the-Hill, and trained in theatre (1947-1949) at the Ada Foster Stage School.
Educated at St Dominic's Convent, Harrow-on-the-Hill, northwest London, she trained for the stage at the Aida Foster School and made her first appearance as a child in 1948 as Moritz in The Burning Bush at the New Lindsey Theatre.
For the last 20 years she lived off Wimbledon Common in the house where she nursed her sick husband, the actor/writer Alan Downer, until his death in 1995. The stress of caring for him brought on her own serious illness but she recovered.
Her father was a musician who abandoned the family when she was 8.
Lifelong friend of "Carry On..." star Joan Sims, they first met when they were 16.
Made her Broadway debut as Dulcie, Polly's friend, in the musical "The Boyfriend" when the London production transferred to New York in 1954. She co-starred with Julie Andrews (as Polly) and the two shared a Manhattan apartment for the duration of the run.
Owns Betty E. Box's white leather script holder.
Replaced Joan Sims in Carry on Cruising (1962) three days before filming commenced. The producers rushed Dilys around London in order to get her fitted with costumes in time.
Son is Agent / Producer / Actor Andrew Downer.
Took over the Flo Castle role from Joan Sims in Carry on Cruising (1962).
Was allowed to keep most of the costumes she wore in the Carry On films, in particular. Carry on Cruising (1962) and Carry on Camping (1969).
Was taught poker by Sid James during the filming of Carry on Camping (1969).