Next month marks the 21st anniversary of Margaret Thatcher's enforced resignation as Prime Minister. It is now more than 30 years since she first gained power. She was not, of course, the first woman to lead a major country. That honour fell to Indira Gandhi in India and Golda Meir in Israel. But along with Gandhi, Thatcher's 11 years at the top make her the longest-serving woman prime minister the world has seen. The strange thing is that despite the advancement of women in business and the professions and the growing numbers of women entering politics in leading Western countries,...