My friend was a public schoolboy who, a few years before, had been badly wounded as a National Service officer in Korea. He had continued to believe in Britain as a place in which fairness, honesty and moderation prevailed. Now he was making discoveries. The policeman lashed out with his baton and leaned down to drag him away. I held him round the waist, my own legs wrapped round a bollard, and in a moment the melee swept the horseman into the chaos of struggling people and swaying placards.
We had all been making discoveries, that October and November 40 years ago. Suez was a turning point, for Britain's self-understanding as a Power in the world but also for my generation's attitude to the state. Labour voters as most of my friends were, we had not imagined that even a Tory government would lie to the world and its own people in order to invade a country which had done no more than nationalise a canal and threaten "British imperial interests".
Now we knew better. A whole mental structure, the dullish, decent expectations of the welfare state, fell apart. Lawless aggression, which ranged up and down the rest of the Cold War world and, against which Britain had seemed to mount a sure defence, was at home in our country, too. We felt then that Suez had changed everything, and all the revelations since have only confirmed that we were right.
In Downing Street, the Cabinet could hear the crowd as they met. But Anthony Eden and his men decided to go ahead. British and French troops were already at sea, and would land at Port Said next day. Outside, we chanted "Law, not War!" But Eden had chosen war, and it was too late to turn back.
President Nasser had nationalised the Suez Canal on 26 July. Eden, already dismayed by the weakening of British authority in the Middle East, supposed that the canal was still Britain's imperial lifeline to Asia, East Africa and the Gulf. Nasser, he declared, had put "his hand on our windpipe". He resolved to use force, and through the summer sought vainly to provoke Egypt into some act that would justify military intervention. When that failed, he decided that the pretext would have to be manufactured.
On Sunday, 14 October, General Maurice Challe arrived at Chequers. On behalf of the French government, he proposed a collusion plot with Israel. The Israelis would invade Egypt. Britain and France would instantly declare the freedom of navigation to be in danger and issue an ultimatum to Nasser which he could not accept. An Anglo-French force would intervene "to separate the combatants", dethrone Nasser and return Egypt to European hegemony.
At the fatal meeting at Sevres on 24 October, Selwyn Lloyd, the Foreign Secretary, signed a secret treaty with France and Israel. The Israeli attack came five days later.Next day, Eden issued two ultimata, one to Egypt and another - fraudulent - to Israel. The RAF began to bomb Egypt on 31 October. Troops landed at Port Said on Monday, 5 November.
Outside the inner Cabinet, few people knew the awful secret of collusion. One was a journalist. Incredibly, Eden unveiled the Challe plan to Iverach McDonald, foreign editor of the Times. Perhaps he thought the Times would burst out cheering. But McDonald was appalled. In his book Eden, Suez and the Mass Media (IB Tauris 1996), the historian Tony Shaw reveals that McDonald told only his editor, William Haley, who was almost as shaken as he. Until then, the paper had supported Eden. Now it backed off and sat on the fence.
The full truth about Sevres took years to leak out. And yet many people knew instinctively what had happened as soon as news of the Israeli offensive broke. This was because Britain was already deeply divided. Half the country took at face value Eden's propaganda depicting Nasser as the Arab Hitler and arguing that to give into him over the canal would be an act of appeasement on the scale of Chamberlain's surrender to Hitler at Munich in 1938. But the other half, growing more alarmed and suspicious week by week, condemned Eden's threat of force as hysterical.
The protesters conceded that Nasser was a repressive autocrat, but a Fascist dictator bent on world domination he was not. Moreover, he was within his rights when he nationalised the canal, and the dispute between Britain and Egypt should be settled by mediation, if possible through the United Nations, rather than by war.
At the time I was living in Manchester, a lodger in the house of the Canadian economist Harry Johnson and his wife Liz. Canada played a noble part through the Suez crisis, vainly trying to talk Eden down from his madness and using all the influence it could muster in London to persuade the British that the Prime Minister was leading the country into disaster. For Harry and Liz, as North Americans, war was a ghastly and unnecessary accident. This had never occurred to me. Like the Manchester people I mixed with, I had assumed that life had a sort of seasonal rhythm in which peacetime and wartime alternated, as night succeeded day or winter followed summer. The man in the pub who had received his call-up papers said: "My grandad had to go in his time, and my dad went in the last war. Now it's my turn."
A patient, long-suffering old Britain was preparing once more to do its duty. British soldiers were going into action, and every loyal man and woman - whatever their inner doubts - should rally round the flag. For people like that, Hugh Gaitskell's anti-Suez appeal on the radio, delivered on the eve of the landings, was an act of treason.
But there was another Britain, too. A Gallup poll at the time of Eden's ultimatum showed that only 37 per cent thought it right to invade Egypt, while 44 per cent thought it wrong. Given the months of anti-Nasser propaganda, eagerly taken up by the entire press with the exception of the Observer, the Daily Herald and the Manchester Guardian, this was an astounding result. For the first time in living memory, Britain was rent apart on a matter of peace and war. The split ran through families, through school playgrounds and university common rooms. The rows over the Abdication or Munich had been nothing to this.
Part of the reason was Hungary. On the Sunday of the demonstration in Trafalgar Square, Soviet tanks drove back into Budapest. I travelled down from Manchester for the Suez rally, and, as I came out of Euston, I saw the head of a procession. The people walked in silence, apart from their soft footfall on the roadway. In front walked a young woman carrying a red, white and green banner with a hole cut out of the middle. Rank after rank passed without a glance or a word, wrapped in their own agony.
We thought then that we were guilty, too, that Suez had made it possible for the Soviet Union to crush the Hungarian Revolution. Many Hungarians agreed. They told Charles Wheeler of the BBC to get out before the Russians cut the Vienna road, and added: "Remember to tell your people that you and the French have wrecked our revolution." This was almost certainly wrong; Khrushchev would have acted as he did with or without the Suez diversion. But Hungary was on the conscience of those who stood up against Suez.
In retrospect, I see that the anger which burst through over Suez had deep roots. Britain in the 1950s was not as placid as it seemed. The wartime rhetoric about national unity and sacrifice was still used to keep us in our place, but its credibility was leaking away by 1956. The shattering of trust in government was followed by the crumbling of other certainties. Unemployment returned. So did inequality, and the opportunity to make fortunes legally. The entrepreneur was promoted from spiv to patriot.
The myth that Britain was still a world power collapsed, as American financial sanctions forced Eden to choose between withdrawal from Egypt and the death of sterling. The self-inflicted wound to British interests in the Arab world took a generation to heal.
In Whitehall, there were old men shouting: "Who's got the ball-bearings? Throw them under the horses' hooves!" We, the young, stared at these veterans of pre-war riots. They had never for a moment thought of "our" government or "our" policemen. For them, British history had always been a merciless struggle between "them" and "us", fought with truncheons, money and lies. In the Suez days, for a terrible moment, we began to see what they meant.