Asherson's serendipitous casting as French Princess Katherine in Henry V (1944) was the result of Olivier fearing that 'Vivien Leigh was too big a star and might eclipse his own performance in the title role'.
Trained for the stage at the Webber Douglas Academy of Dramatic Art. Made her theatrical debut in a walk-on part in John Gielgud's 1935 revival of Romeo and Juliet at the New Theatre.