Sketch: Obama in London was an American Invasion on Whitehall

The grey skies outside were the only reminder you were still in Britain as the US mounts a special ops takeover of the Foreign Office

David Cameron holds a joint press conference with Barack Obama, at the Foreign and Commonwealth Office following a bilateral meeting in Downing Street (PA)

No one was pooling any sovereignty down at the Foreign Office. This was a full on hostile takeover.

Back when Abraham Lincoln was too busy emancipating to make any meaningful scramble for Africa, India or anywhere at all really, about three quarters of the population of the earth was governed within these whitewashed walls at the bottom of Whitehall. But not on Friday. This was a full on regime change. Shock and awe.

Only the grey skies, the chill wind and the sideways rain outside gave any reminder that we were all still in Her Majesty’s United Kingdom. The lowly British Westminster press corps suddenly knew what it felt like to be Vietnamese in the 1970s. Or Korean in the 1950s. Or Nicaraguan just about any time since the 1850s. Or Guatemalan, or Iraqi, or Afghan, or Libyan. Or Filipino, or Cambodian. You get the picture.

Admission to the US President and the British Prime Minister’s press conference was by “White House Press Pool” badge only. The White House is 3,622 miles away. Once safely through the metal detectors, men called Schulz and women called Desree bestrode the Foreign Office's Locarno Suite as doth a colossus, but with immaculately sculpted hair that shone like polished granite. The Locarno rooms are named after a town in Switzerland where a conference took place in 1925, to which Mussolini made an understated entrance by speedboat. In the form of the implacable Desree, Il Duce was here in spirit.

“UK on the right. US on the left,” she bellowed as she marched us in, the Wedding Planner From Hell.

David Cameron spoke first. If you follow the television pictures closely enough, there is a slim chance you might find one member of the hundred strong audience become very briefly turn their head in his direction but this cannot be guaranteed. Not when there's an Obama to stare at.

The President had written in his opinion piece in Friday morning’s Telegraph that the people of America would be taking a “deep interest” in Britain’s EU referendum, and this was very much reflected in the enquiries made of him by the American press corps, one of whom deftly demanded answers on Vladimir Putin, transgender laws in North Carolina and the death of Prince in a single sentence. Another was just as keen to to know about Libya and Hiroshima.

It had been suggested by the more deranged end of the Brexit camp that a visiting US President should not be allowed to give his opinion on the referendum question, as if depriving those of us with a vote to cast from knowing what our oldest and most important ally thinks on the matter is a helpful thing to do. For this, the President had a sharp, but obvious answer.

“I’m not coming here to fix any votes,” he said. ”I’m offering my opinion. In democracies everybody should want more information not less.”

The main charge against him has been that, here he is, President of the USA, demanding that the British should sacrifice their right to govern themselves in a way the US would never accept. On this, he was similarly ambiguous.

“If I’ve got access to a massive market, where I sell 44 per cent of my exports,” he patiently explained, smiling as he did so. “And now I’m thinking about leaving the organisation that gives me access to that market, that is responsible for millions of jobs, and commerce on which businesses depend. That’s not something I’d probably do.”

It was at this point that the British side glanced over the aisle with sympathy. How have they put up with this short-sighted lunacy for eight years, without the wisdom of Nigel Farage to keep them sane?

But would the Special Relationship survive Brexit? “Nothing will impact the emotional and cultural and intellectual affinities,” he said. “[But] our focus will be on negotiating with a big bloc. And the UK is going to be at the back of the queue.”

I’ll still send you a Christmas card, but there won’t be a fiver in it.

The effortlessness with which the case for Brexit was dismantled was worrying in its way. With two months til the referendum, that job now falls to David Cameron and, in theory, Jeremy Corbyn.