After another set of empty offices and meeting rooms, they reached a level low enough that no sniper, no matter how skilled, would be able to angle a shot into the basement from it.

Knox checked his watch. ‘Fifteen minutes before they’re due to finish.’

‘Better hope they’re not early for that too,’ Bennett replied. ‘I’ll go see if anyone’s loitering outside or twitching blinds on the other side of the street.’

They split up in the foyer. Knox watched Bennett walk back out into Great Russell Street, hoping there wasn’t a hidden sight trained on her, then went down the wide spiral staircase that led to the underground conference hall.

Two guards stood outside the large doors Kosygin and Woodcock were on the other side of, discussing the finer complexities of combining socialism and unionism. Knox stood in line with them, snatching glances at both while listening for any commotion in the room beyond.

After five minutes of quiet murmuring he heard the sound of scraping chairs and moving feet. Then the doors opened and Aleksei Kosygin and George Woodcock walked past Knox, each followed by a small coterie of advisers. It was the first time he’d seen either man in the flesh, and he was struck by how normal Kosygin seemed, and how farcical Woodcock’s famously bushy, unkempt eyebrows made him look.

Knox fell into step with the two guards and followed the group up to the ground floor and out onto the street where three diplomatic Volgas were waiting. He tensed his muscles and held his breath, ready to lunge forward and shove Kosygin to the ground at the slightest noise. But there was no shot from a window, no shouts to take cover, and no explosion when Kosygin got into his car.

Knox watched the small Soviet motorcade pull away from the kerb and be quickly replaced by his Jaguar. He got into the passenger seat, and let Bennett tail the Russians all the way across the city to Kensington Palace Gardens, the wide street of mansions between Notting Hill and Kensington better known as Embassy Row, without incident.

‘I don’t like this,’ Knox said, between bites of a sausage sandwich and gulps of weak coffee in a cafe on Notting Hill Gate, shortly after he and Bennett had watched Kosygin disappear behind the fence of the Soviet embassy.

‘It could use some mustard,’ Bennett said. ‘And the coffee’s so bad it’s almost American.’

‘But it gets the job done,’ Knox replied with a grin, before adding, ‘I meant having no idea when the KGB is going to strike.’

‘I know,’ Bennett said, as she gave up on her sandwich and pushed her plate away from her. ‘At least we’re on the same side again. And it’s nice we can be pretty sure we aren’t the bad guys.’

‘There is that,’ Knox said.