It was one of the key events of the 20th century. Thirty years ago, religious leader Ayatollah Khomeini returned to Iran from exile and launched an Islamic revolution. The BBC's John Simpson was on the plane that flew the Ayatollah to Tehran.

When the revolutionary disturbances of 1978 broke out, Ayatollah Khomeini was being kept under tight control as an exile in the Shia holy city of Najaf, in Iraq.

Iraq was already being run by Saddam Hussein. Then the Shah of Iran asked Saddam to expel him.

It was a catastrophic misjudgement. The Ayatollah flew to France, and could suddenly speak to the entire world.

When the Shah eventually left Iran, in January 1979, the way was open for the Ayatollah to fly home and overthrow the imperial system.

Then we landed, and the Ayatollah was greeted by what some say is probably the largest crowd in human history.

The Islamic Republic was duly established in Iran; Muslim opinion around the world was galvanised; and a major new focus of opposition to Western liberalism took shape.