‘What the hell’s going on?’ Georgina was by my side, her impressive bulk providing me with something to shelter behind. A girl tripped and fell, spreadeagled at our feet, laughing.

‘Come on, everybody! Clap your hands!’ The voice, amplified by the microphone, was only too familiar. We turned and registered that the boy undressing was now revealed as none other than Master Baxter, who had shed the rest of his clothes, and was cavorting wildly round the stage in his underpants and looking in grave danger of losing even those.

By now the ballroom was bedlam. Some people must have escaped at the first signs of trouble, with that marvellous instinct that the British upper classes generally display in such a situation, but those who were not at the exits already were finding it increasingly hard to get to them. Suddenly I caught sight of Terry, in the midst of the demented crowd. Her hair had collapsed and a separate arrangement of ringlets had detached itself from her head and somehow got caught on a zip or hook fastener behind her neck, leaving a kind of mane to sweep down her back, making her look faintly feral as she attempted to claw her way through the ranks of her guests. I reached across a weeping man with his regurgitated dinner down his front and caught her wrist, pulling her through the crowd towards us. ‘What is it? What’s happening?’

‘Somebody spiked the brownies. They were full of hash.’

‘What?’ Is it to be believed that the word was not immediately familiar to me? Or was it just the shock of discovery blocking my concentration?

‘Hash. Marijuana. Dope.’ Terry was altogether more at home with the topic, if angrier than Genghis Khan.

‘Why? Who would do such a thing?’

‘Someone who wanted to ruin my party and pretend to themselves it was a joke.’ This was, I have no doubt, a completely accurate diagnosis. She was rich, she was good-looking, she was an outsider. That was more than enough to ensure enmity in several quarters, although this seemed an unusually unpleasant way of demonstrating it. Then again, the perpetrator may not have been aware of the level of mayhem that would ensue from their jolly prank. We were not all experts then.

‘You seem OK.’

‘I’m OK because I’m on a diet.’ She said it snappily and it was almost funny, if we had not been in the middle of such desolation. At that moment a weeping Verena Vitkov claimed her daughter from the other side. Someone had trodden on her dress, and it had torn away from a seam at the waist, leaving not her legs but her roll-on exposed, which was of course much worse.

‘Let’s get out of here,’ I said to Georgina and she nodded, but then two things happened. The first was that I could see Serena Gresham had climbed on to the stage with a dinner jacket, presumably Damian’s, which she was trying to wrap round him despite his protests. She also had his trousers over her arm but obviously that task was a bridge too far and she didn’t even attempt it. The second thing to catch at our attention was the sound of a police whistle, which echoed through the chamber like the shrill tolling of Doom. At once, what had already been chaos was transformed into a panicking stampede. It is easy now to think, almost calmly, of the notion of a drugs raid. In the forty years that have elapsed since these events, drugs themselves have ceased to seem extraordinary. Regrettable, I would hope, and something to be avoided for most of us even today, but no longer weird. In those days the vast majority of this crowd were strangers to the very notion. Whatever the impression that pop stars and Channel Four like to give of the Sixties, if their tales are true, which I often doubt, they were operating in a different world from my bunch. Obviously the bad boys among us were starting to experiment and by seven or eight years later a lot of us would have been introduced to the whole trendy culture of drugs and damn-it-all, but not by then. After all, most of what came to be called ‘the Sixties’ happened in the following decade. Yet here we were, debutantes and beaux, plus many of their mothers and fathers, in a full-scale drugs raid, which would provide, as we were only too aware, a perfectly wonderful story for the papers the following day. Out of family loyalty, if nothing else, all those nice, young sons and daughters of earls and viscounts, of high court judges and generals, of bankers and heads of corporations, had to get out of that room unseen and unapprehended, to stop their blameless daddies being soaked in the spray of public ridicule that was even then being loaded up, ready to flow. If the room had been on fire there couldn’t have been a more urgent dash for the door.

I too would have headed in the same direction as the crowd, but Georgina held me back. ‘It’s hopeless,’ she said. ‘They’ll be waiting for us on the pavement.’

‘Where, then?’

‘This way. There’ll be a service exit for the group. And the maids must have been bringing the drinks up from somewhere.’

Together we pushed against the crowd. I glimpsed Candida Finch, green-faced and at the end of her tether, leaning against the opposite wall but she was too far away for me to help her. Some girls were dancing a sort of reel, accompanying themselves with alternating screams, in the middle of the floor between us. Then Candida was swept away and I didn’t see her again. ‘This is a nightmare.’ Serena was nearly upon me when I realised who it was. She had an arm round Damian, who was still ranting and calling out to everyone to clap their hands. ‘I’ll clap your hands if you don’t shut up,’ she said, but it didn’t seem to have much effect. Damian fell, and others surged over him, until I really began to wonder if he would be seriously injured. ‘Help me get him up.’ Serena was down among the lunging feet and I knew I had to do my best. Together we managed to hook our arms under his and literally drag him to the edge of the room.

‘Why are you all right? Didn’t you eat any either?’

Serena wrinkled her nose. ‘I wasn’t hungry.’

‘Here we go!’ The enterprising Georgina had found a service door at the back behind a curtain that a few people, but not many, were taking advantage of. Behind us, the whistles and general shouting had increased in volume, and it was clear that those who had tried to leave in a more orthodox manner were being subjected to hideous humiliations before they were allowed to do so.

‘My God, the press is outside!’ This from Lucy, who had started down the main stair, only to make this unwelcome discovery and beat a retreat whence she had come. ‘If I get in the paper my father will kill me.’ It’s funny. We were so much more governed by these considerations than our equivalents are now.

Following our leader, Georgina, we came to a landing at the top of a stone, service staircase. Guests in various stages of dishevelment were hurrying down it. One girl broke her heel and fell the remainder of the second flight with a scream, but without pausing she scrambled up, tore the shoe off the other foot and plunged on. Unfortunately, Damian seemed to be getting worse. He had now ceased his requests for us to clap our hands and had decided instead simply to go to sleep. ‘I’m perfectly all right,’ he murmured, his chin sinking deeply into his chest. ‘I just need a little shut-eye and then I’ll be as right as rain.’ Down went his chin even further, followed by his eyelids, and he began to snore.

‘We’ll have to leave him,’ said Georgina. ‘They won’t kill him. He’ll just have his name taken, and a warning or something of the kind, and that’ll be the end of it.’

‘I’m not leaving him,’ said Serena. ‘Who knows what they’ll do? And what happens afterwards? If he has his name on a list at a drugs raid, he might never get a passport or a security rating or a job at an embassy or anything.’ This string of words, flooding out as they did, created a rather marvellous contrast to the life we were leading at that precise moment, cowering on a dingy, back stairway, on the run from the police. It conjured up images of embassy gatherings at which Damian would shine, and foreign travel and important work in the City. I found myself wishing that Serena had voiced such fragrant worries about my destiny.