What brought about Margaret Thatcher's downfall?

Baroness Thatcher, Britain's first female premier, was Conservative prime minister from 1979 to 1990 and won three successive general elections.

She has died "peacefully" after suffering a stroke while staying at the Ritz hotel in central London.

In the third of four Newsnight films, Martha Kearney considers what brought an end to Margaret Thatcher's political career - not the unions or the opposition or the electorate, but the Conservative politicians closest to her.