A voice piped up behind them: ‘Hey, can you hurry it up along there? We want to get in before midnight.’

The guard waved him on. ‘Thank you, sir. Enjoy your evening.’

Tom moved up the stone steps and, once inside, instinctively scrutinized the layout. The hall was dominated by a grand, sweeping staircase, with a balustrade of wrought iron. The vast reception room ran the depth of the house to the french windows that opened onto another terrace and garden at the rear. The drawing room was to the right, the state dining room to the left, the kitchen and staff offices evidently beyond.

The strains of some Bach wound their way through the crowd from a chamber orchestra. A greeter swooped down on him. ‘Hi, my name’s Charlie. Can I help you with anything tonight, sir?’

‘You could tell me the order of ceremony.’

‘Sure. So, in about a half-hour the President will be joining us for a few minutes’ walkabout. Then, with your prime minister, he’ll do a short welcome speech and there’ll be a line-up for a few handshakes with selected guests.’

‘How do I get on the list for that?’ Tom wasn’t too fussed about meeting the prime minister, but it wasn’t every day you got to shake hands with the President of the USA.

‘Aw, I’m real sorry. That won’t be possible this time.’ Charlie looked genuinely disappointed on his behalf. ‘The President and prime minister’s staff do the list. It’s prepared well in advance.’

‘Of course. As long as I get to see them, I’ll be happy.’

A waiter with a tray of drinks swept towards him. ‘We have a Californian champagne from Sonoma County.’

Tom knew that wines from outside that region of France weren’t called champagne, but let it pass.

‘And a very fine 2007 rosé from Gloria Ferrer.’

Tom declined. He needed to keep his head clear. ‘I’ll take a Coke, please.’

But he could sample the food: orange morsels of Alaskan salmon – so said the woman in the Stars-and-Stripes waistcoat serving it – with pickled ginger on ‘wild rice blinis’, seemingly some kind of tiny pancake. Another was carrying a tray of dates stuffed with almond, wrapped in bacon. Pass on that one. He swallowed two of the salmon things, then took a mini steak sandwich with a little American flag on a cocktail stick in it. Not bad.

‘They’re steak and Stilton,’ explained the waitress, ‘to represent the Special Relationship between Britain and the United States.’

And sure enough, after the delicious steak, an un-welcome lump of cheese dissolved on his tongue. Special Relationship – perhaps, in an unsubtle, blundering way.