Margaret Thatcher had voice training to make her sound more authoritive.
Here are 2 clips the first from 1975 and the second from 1987.
They don't sound a whole lot different to me
http://www.youtube.com/watch?v=oK3eP9rh4So
http://www.youtube.com/watch?v=0vIt9lRzuFE&feature=relat...