Thatcher was on a visit to Pakistan in October 1981 and, after visiting some of the many hundreds of thousands of Afghans gathered in refugee camps there, had been taken by Pakistani leader General Mohammad Zia-ul-Haq through the Khyber Pass to see the Afghan border.
While there, the leaders approached a border crossing and reportedly shook hands with the surprised guards on the Afghan side.
"We had better leave while they're friendly," Thatcher was quoted as saying.
WATCH: Margaret Thatcher and Zia-ul-Haq visit the Afghan-Pakistani border.
As noted in the TV report above (at about the 2:30 mark), Thatcher probably wandered a few meters inside Soviet Afghanistan territory.
The Kremlin responded to the whole incident by blasting Thatcher's "provocation aimed at stirring up anti-Soviet hysteria."
But in hindsight, the episode can be seen in the light of what Ishaan Tharoor at "Time" magazine describes as Thatcher's foreign policy falling on the "wrong side of history":
Or as the "Montreal Gazette" report notes, in its reporting of Thatcher's visit to Pakistan, the Soviet TASS news agency "repeated accusations that the United States and other Western countries are arming the Afghan rebels."
-- Dan Wisniewski