Last modified on Fri 14 May 2021 09.02 EDT Exhibition of the week Eileen Agar One of the most imaginative and quirky early 20th-century British artists gets a fresh look â is Agarâs seaside surrealism due a revival? Whitechapel Gallery, London from 19 May until 29 August. Also showing Jean Dubuffet Wildly subversive star of postwar French art whose concept of art brut â raw art â is suddenly urgent again in our age of authenticity. Barbican, London from 17 May until 22 August. Becket This is a beautiful and exciting encounter with the lost world of medieval Britain, packed with fascinating art. British Museum, London from 20 May until 22 August.