In December 1941, the National Service Act (no 2) made the conscription of women legal. At first, only single women aged 20-30 were called up, but by mid-1943, almost 90 per cent of single women and 80 per cent of married women were employed in essential work for the war effort.

https://www.bbc.co.uk/history/british/britain_wwtwo/women_at_war_01.shtml