Margaret Thatcher was Britain's first female prime minister, she came from an ordinary background to hold that office and dominate British politics for over a decade. Even her fiercest opponents do not dispute that she made a huge impact. By contrast,
Tony Benn was the son of a hereditary peer whose politics and views were not just rejected by the public but by his own party over two decades before he left Parliament. The achievement and significance of the two are hardly comparable. Longevity doesn't equal significance.