The subject of the stamp is Marie Stopes, best known for opening Britain's first family planning clinic in 1921 and later hailed as a pioneer for women's reproductive freedom. But in the 1930s, Stopes revealed herself as a supporter of eugenics, a pseudo-scientific racial theory adopted by German Nazi scientists, The Times of London reported Tuesday.

The stamp honors Stopes as one of a series issued to commemorate British women of achievement. But critics point out that Stopes, who died in 1958, openly advocated sterilization of those deemed "unfit for parenthood," including the mentally ill and alcoholics, and professed admiration for Adolf Hitler on the eve of World War II.

The Rev. Peter Mullen, chaplain to the London Stock Exchange, is among the critics. He told The Times: "She campaigned to have the poor, the sick and people of mixed race sterilized."

"These stamps commemorate six unique individuals whose dedicated work not only changed the lives of other women, but society as a whole," replied Juliette Edgar, head of special stamps at the Royal Mail.