Ann Williamson was born in Oxford on 19 November 1922, to Herbert Stansfield Williamson and Winifred Lilian Williamson. Herbert had previously worked in the Indian Civil Service; Winifred had helped organise one of the first family planning clinics in Britain. Williamson gained a scholarship to Headington School, Oxford from 1930 to 1939, before winning a place to study mathematics at Lady Margaret Hall, University of Oxford, between 1940 and 1943. At the time relatively few women went to Oxford and even fewer studied maths. There were only five women in her year at Oxford and she remarked that the men coming to university had been taught maths much better at school than the girls. Indeed, it was suggested to her by the headmistress of her school that studying maths was "unladylike"; her parents had to overrule her school to allow her to take up her place at Oxford.
Williamson was recruited to work at Bletchley Park in September 1943 after she graduated from Oxford, and until May 1945 she worked in Hut 6 on German Army and Air Force Enigma decryptions. She was recruited as a temporary worker with the Foreign and Commonwealth Office on an annual salary of £150. Much of her work involved converting 'cribs' into 'menus', the operating instructions for the Bombe decryption devices to identify what that day's Enigma settings might be. The Germans changed their code every night at midnight so Williamson and the others had then to restart trying to crack the codes. Stuart Milner-Barry, the head of Hut 6, had difficulty recruiting enough men due to war demands and British civil service rules prevented men and women from working together on night shifts so Williamson worked solely with women in Hut 6. After the war, like others who worked at Bletchley, she was instructed to forget about her work there and never to talk about it. Once the work at Bletchley became public and the ban was lifted she gave many illustrated talks and interviews about her wartime role. Her story is included in the book The Bletchley Girls: War, Secrecy, Love and Loss: The Women of Bletchley Park Tell Their Story by the historian Tessa Dunlop.
Academic and social policy work
In the 1950s she worked as a marriage guidance counsellor with the Scottish Marriage Guidance Council. In the 1970s she returned to university to study social policy and in 1980 she graduated with a Master of Philosophy from the University of Edinburgh. In the early 1980s she was research associate at the Department of Social Administration in the University of Edinburgh. Mitchell worked and published extensively on the subject of marriage breakup and divorce, and in particular on children's experience of family breakup. Her books include Someone to Turn To: Experiences of Help before Divorce ; When Parents Split Up ; Children in the Middle ; Coping with Separation and Divorce ; and Families. They have been translated into a number of languages. Mitchell's work is referred to in several works on divorce in Scotland and further afield, and was used as supporting evidence in two reports by the Scottish Law Commission, "Family Law: Report on Aliment and Financial Provision" and "Report on Reform of the Ground for Divorce". In 2014, in an article in the Scots Law Times, the family law barrister Janys Scott QC reviewed Mitchell's work on the workings of the Scottish divorce court. Scott concluded that "Mitchell has had a profound influence on family law in Scotland", and that her 1985 book Children in the Middle was "a seminal work" in the field.
Historical research
In her seventies, Mitchell researched and wrote about the history of Edinburgh. She published two books, The People of Calton Hill and No More Corncraiks: Lord Moray's Feuars in Edinburgh's New Town.
