What were members of the women's social and political union called?

They were called suffragettes because of, well, the woman's "suffrage" they were fighting for.
The Women's Social and Political Union (WSPU) was the leading militant organisation campaigning for Women's suffrage in the United Kingdom, 1903–1917. Its membership and policies were tightly controlled by Emmeline Pankhurst and her daughters Christabel and Sylvia (although Sylvia broke away).