Very early in life, her father discovered that Flora had a talent for recitation and from the age of six, she was taken around by horse and carriage to recite, and to compete in recitations. She grew very used to winning and was always distraught if she lost. She was educated at the Palmers Green High School.
Both the BBC and ITV made special programmes to celebrate her 80th birthday. Her private life was largely focused on her large family of sisters, nephews and nieces, who used the home in Wykeham Terrace, Brighton, which she shared with sisters Darge and Shela, as a hub of activities.
Robson made her stage debut in 1921 at the age of nineteen. Standing 5 feet 10 inches (1.78 m), but decidedly lacking the glamorous looks of a leading lady, she specialized in character roles, notably that of Queen Elizabeth I in both Fire Over England (1937) and The Sea Hawk (1940). At the age of thirty-two, Robson played the Empress Elizabeth in Alexander Korda's Catherine the Great (1934). She was nominated for the Academy Award for Best Supporting Actress for her role in Saratoga Trunk (1945). After the war, demonstrating her range, she appeared in Holiday Camp (1947), the first of a series of films which featured the very ordinary Huggett family; as Sister Philippa in Black Narcissus (1947); as a magistrate in Goodtime Girl (1948); as a prospective Labour MP in Frieda (1947); and in costume melodrama, Saraband for Dead Lovers (1948). Her success in Hollywood brought her wider recognition.
She was created a Commander of the British Empire (CBE) in 1952, and raised to Dame Commander (DBE) in 1960, an award which was partly for her charity work, largely un-noted, which she carried on until her death, often for small and rather obscure charities rather than the grand ones which would have given her more publicity. This was part of her Christian upbringing and her sense that she should "give something back". She was also the first famous name to become President of the Brighton Little Theatre.
She died in Brighton of cancer at the age of 82, never having married or had children. The sisters with whom she shared her life and her house died around the same time: Shela shortly before her in 1984, and Margaret on February 1 1985. There is a plaque on their house in Wykeham Terrace, Dyke Road, Brighton, and also one in the doorway of the church of St. Nicholas, just up the hill from their house and of which Flora was a great supporter. In 1996, the British Film Institute erected a plaque at number 14 Marine Gardens, location of Flora's other Brighton home, where she lived from 1961 to 1976.