On 21 April, as the British task force approached the islands, US secretary of state Al Haig told the British ambassador to Washington, Sir Nicholas Henderson, he intended to inform the Argentine junta that UK troops would be landing on South Georgia, the first of the islands to be seized by the Argentines.

Mr Haig, who had been trying to broker a settlement, insisted it was the only way he could keep his diplomatic initiative alive.

“If the Americans acted in this way, they would be able to show even-handedness to the Argentinians and this would enable them to continue their role as go-between,” he argued.

Sir Nicholas was appalled. He told Mr Haig he was going far beyond the obligations of a neutral negotiator and that the information could be used by the Argentines to mount a submarine or suicide air attack on the task force.

Reluctantly, Mr Haig promised to keep quiet.

That said, let us not forget that U.S. diplomacy over the Falklands was not adroit thirty years ago either, though at least in the end Reagan did the right thing:

“I wonder if anyone over there realises, I’d like to ask them. Just supposing Alaska was invaded …” asked Thatcher. “Now you’ve put all your people up there to retake it and someone suggested that a contact could come in … you wouldn’t do it.”

“No, no, although, Margaret, I have to say I don’t quite think Alaska is a similar situation” said Reagan.

“More or less so,” snapped Thatcher. Reagan feared the pending rout of Argentine forces in the south Atlantic would destabilise the region, damaging Washington’s battle against left-wing regimes in Latin America.

But Thatcher, with barely concealed impatience, scotched the plan with a verbal explosion. Reagan could barely get a word in as the prime ministe gushed out a torrent of dismissal. “I didn’t lose some of my best ships and some of my finest lives, to leave quietly under a ceasefire without the Argentines withdrawing,” she said.

“Oh. Oh, Margaret, that is part of this, as I understand it …” stammered Reagan, trying to outline a Brazilian peace plan. It called for a ceasefire, Argentine withdrawal and a third-party peace-keeping force in the disputed islands. “Ron, I’m not handing over … I’m not handing over the island now,” insisted Thatcher. “I can’t lose the lives and blood of our soldiers to hand the islands over to a contact. It’s not possible.

“You are surely not asking me, Ron, after we’ve lost some of our finest young men, you are surely not saying, that after the Argentine withdrawal, that our forces, and our administration, become immediately idle? I had to go to immense distances and mobilise half my country. I just had to go.”

The conversation recorded in Washington took place on May 31, 1982, after paratroops had taken Goose Green and were poised with other troops for the final assault on Port Stanley. The State Department was worried that the British advance looked too much like American-backed “colonialism”.