Mary Law, actress who among many roles enjoyed two spells as the lead in The Mousetrap – obituary

Mary Law with Agatha Christie celebrating the sixth year of The Mousetrap in 1958
Mary Law with Agatha Christie celebrating the sixth year of The Mousetrap in 1958 - George Elam/ANL/Shutterstock

Mary Law, who has died aged 91, had two stints playing the anxious guest-house proprietress Mollie Ralston in Agatha Christie’s long-running West End show The Mousetrap; she was also a stalwart of 1950s television, becoming the first British TV actress to go into space – as the science student Janet Campbell in the children’s series The Lost Planet (1954) – and making a fleeting appearance in the hospital soap opera Emergency Ward 10.

With blue eyes, blonde hair and a strikingly expressive face, Mary Law became the fifth actress to play Agatha Christie’s leading lady when she joined the cast of The Mousetrap in 1956. She was still in the role when the show reached its 1,998th performance in September 1957, making it the longest-running straight play in the history of British theatre. It continues today,  having now clocked up almost 30,000 performances.

Having left The Mousetrap in 1958, she returned a year later to make a guest appearance when the play was staged in Wormwood Scrubs; towards the end of the performance two prisoners managed to break out. Mary Law also recalled with some alarm how during an on-stage tussle the captive audience yelled: “Kill her! Kill her!”

In The Mousetrap, 1957
In The Mousetrap, 1957 - Alamy

Her most memorable film appearance was in the 1960 comedy Carry on Constable, playing a shop assistant who suspiciously eyes up Kenneth Williams and Charles Hawtrey’s bumbling rookie policemen disguised as female shoppers.

“I always remember Charlie Hawtrey coming to ask me how to wear a pair of very high heels and walk properly,” she told the nostalgia website Retroboy, adding that most scenes were captured in a single take. “I had to spend a very tiring morning running after [Hawtrey] and Kenneth Williams somewhere in London.”

Mary Elisabeth Law was born in Croydon on September 23 1932, the only child of Oliver Law, an architect, and his wife Marjorie “Madge”, née Nutter, an enthusiast for amateur theatricals. Mary’s wartime memories included seeing streams of white vapour and black smoke from bombing or dogfights in the skies over the Sussex Downs, where she would go riding.

As a child she wanted to be a dancer until being enchanted by A Midsummer Night’s Dream. She produced her first plays while at schools in Worthing and West Chiltington and after attending the Royal Academy of Dramatic Arts made her debut at Regent’s Park Open Air Theatre in Shakespeare productions directed by Robert Atkins. “We had to compete with the roaring of the lions from the zoo,” she recalled.

Mary Law with Kenneth Alwyn in 1960, the year of their marriage
Mary Law with Kenneth Alwyn in 1960, the year of their marriage - ANL/Shutterstock

On television she played a nurse in A Place of Execution (1953) and the Duchess of York in the Shakespeare adaptation An Age of Kings (1960) with Eileen Atkins, Sean Connery and Patrick Garland.

She was also seen with Peter Vaughan in the newspaper series Deadline Midnight (1960) which, like The Lost Planet, was originally broadcast live and in black and white. Later “we went to filming in colour and recording”, she said. Her first film appearance was as an office girl in the comedy romance For Better, for Worse (1954) with Dirk Bogarde.

Mary Law was back on stage in 1955 as one of the three witches in the Royal Shakespeare Company’s Macbeth with Laurence Olivier, and in Dulcie Gray’s Love Affair at the Lyric Theatre, Hammersmith. The following year she played the neurotic wife Kay Strange in Agatha Christie’s slightly less successful murder-mystery Towards Zero, adapted from her novel, before joining The Mousetrap. She returned to the cast from 1975 to 1976, again as Mollie Ralston.

As Kay Strange in Towards Zero at the Theatre Royal, Nottingham, 1956
As Kay Strange in Towards Zero at the Theatre Royal, Nottingham, 1956 - Alamy

Still in the West End, in the mid-1960s she played Lady (Emilia) Dilke to Anthony Quayle’s adulterous politician Sir Charles Dilke in The Right Honourable Gentleman with Anna Massey, Corin Redgrave and Coral Browne. At other times she was in weekly repertory around the country, rehearsing one show in the daytime and performing the other in the evening.

In recent years Mary Law became a passionate environmentalist, campaigning against proposals for fracking close to her home in West Sussex. In her eighties she was volunteering at an animal sanctuary founded by her neighbours Patrick Garland and his actress wife Alexandra Bastedo.

In 1960 she married the orchestral and theatre conductor Kenneth Alwyn in a rain-soaked ceremony at St Paul’s, the actors’ church in Covent Garden. They worked together on occasions, presenting a 1979 Radio 2 series called That’s Entertainment with guests including Tommy Steele, Marti Caine and Max Jaffa.

She also narrated the story of the Second World War for her husband’s 1990 Battle of Britain concert tour of North America, featuring wartime classics with the BBC Concert Orchestra and the Central Band of the RAF.

Alwyn died in 2020 and Mary Law is survived by their daughter, Timandra, who was a child actress. Their other daughter, Lucy, died from a brain tumour last year.

Mary Law, born September 23 1932, died April 15 2024