Thirty years ago this week Chairman Mao's Cultural Revolution was at its height. All over China "counter-revolutionary elements" were being "struggled" - in other words, anyone holding any authority, appearing to have middle-class tendencies or simply not showing enough fervour was liable to be publicly humiliated, beaten or killed out of hand. Later research has shown that in some cases Red Guards ate the bodies of their victims.
In 1967 the frenzy began to be directed against foreigners. The Indonesian embassy in Peking had been sacked and burned, the Mongolian ambassador's car set on fire and the Soviet embassy invaded. Britain became the target when the authorities in Hong Kong, determined to stop the mass demonstrations there, closed Communist newspapers and charged some of their journalists with inciting and participating in violence. An ultimatum to the British embassy in Peking was rejected, and its staff prepared for trouble.
What followed will be remembered by most of the 51 people assembling in the opulent Locarno Room of the Foreign Office for a commemorative dinner on Wednesday. Sir Ray Whitney, Conservative MP for Wycombe, was among the 23 diplomats and support staff in the British embassy on the night of 22 August 1967. "We're not having a Chinese banquet, just noisettes of lamb," he said. "Only a few firms are cleared to cater at the Foreign Office, and the one we chose didn't have anything so exotic on its sample menus."
Some veterans of the Peking siege cannot make it. Sir Len Appleyard is the present ambassador in Peking, Sir John Weston, our man at the UN, is chairing the Security Council this month, and Sir Percy Cradock, Mr Patten's arch-critic, is away. The guest list includes family members in Peking at the time, as well as foreign diplomats who helped the British.
The Red Guards' attacks had driven the foreign community together 30 years ago - despite Cold War hostility, East European diplomats tried to warn the British that a mob was on the way, but the phone lines had been cut. So had radio links to London; as chanting Red Guards set fire to the building and the people inside retreated to the embassy's secure area, the Foreign Office had no way of knowing what was going on.
Finally the 18 British men and five women, led by the senior diplomat, Donald Hopson, had to come out. One described to Anthony Grey, a Reuters journalist himself held hostage in Peking, what happened next. "I have a mental image of the Minister lurching off to one side with blood streaming down his face from a blow... Hands seized us from all sides, punches rained down on us from all directions."
Some of the women were interfered with and had most of their clothing ripped off. Red Guard girls wrenched the testicles of the men as they were frog-marched around. After nearly an hour, People's Liberation Army soldiers lounging at the gate were persuaded to intervene, and all the group got to safety.
No doubt it was Sir Percy's experiences that night which once led him to describe the Chinese regime as "a bunch of thugs", but several veterans of the incident denied hotly that it had continued to affect British policy towards China up to the present day. Some critics claim that the destruction of the embassy - it was rebuilt by the Chinese in 1972 - convinced a whole generation of Foreign Office sinologists that China would go to any lengths to get its way, with damaging effects on negotiations over Hong Kong. This phobia, they say, accounts for the sinologists' failure to see eye to eye with Mr Patten.
"I challenge that," said Sir Ray. "Most office-holders in China today suffered during the Cultural Revolution." "For those of us who went through those events," said Sir David, "[it] was a most vivid reaffirmation of the sheer awfulness of the regime... in the sense of what it could do and what it would allow to happen. What we witnessed then in Peking, including the corpses on the street, was simply extremely distasteful. But I don't think that any of that bears really on what happened subsequently in terms of the handing back of Hong Kong."
No speeches are planned on Wednesday, and no hint of present-day controversy is expected to pollute the tide of reminiscence. But it is a safe bet that if toasts are drunk, there is unlikely to be one to Chris Patten.