Bruce Anderson: Macmillan had the best known reshuffle of all time, but Mrs Thatcher had the most successful reshuffle

Assuming that there is a Cabinet reshuffle in September, we can make one confident prediction. It will neither be as famous as the best-known reshuffle of all time, nor as radical as the most succesful of all reshuffles.

Summer, 1962, and the Prime Minister is worried. It seems to Harold Macmillan that everything is adrift and that wide-reaching changes are necessary to reinvigorate his government. Throughout his long life, Macmillan was prone to hypochondria. At 68, he was feeling at least his age, which - oddly, it might seem - made him less kindly disposed towards the older figures in his Cabinet. He decided that youth was needed, whatever the consequences for the veterans.

Macmillan remains a complex figure. None of his biographers has proved equal to their subject-matter. Throughout his life, he had to endure unhappiness and suffering, to which he responded with stoicism and courage. He was a man of masks: useful for concealing pain. At times, he could give the impression of flippancy and of facile optimism. In reality, he was profoundly religious, believing that faith alone made the human condition tolerable.

His politics were shaped by war, poverty and fear. In the First World War, he was a gallant young officer. He was wounded five times; most of his school and Oxford friends were killed. With a profound emotion which he could rarely express, he came to venerate the bravery that his men displayed. He went into politics to help build a land fit for heroes.

By the 1930s, he seeme to have failed, on all fronts. The Great Depression was inflicting dreadful hardships on his Stockton constituents, and on much of the industrial North. Less than twenty years after the Armistice, the threat of fascism made a mockery of the victors' hopes. His own marriage had virtually disintegrated, and his political prospects were equally blighted. But he fought on and fought back. Twenty years later, he was Prime Minister.

Even so, he retained the convictions born of hardship. He agreed with Lord Beveridge: the duty of government was to ensure full employment in a free society. He was a convinced Keynesian; he did not think that there could be a realistic alternative. But in the 1950s, it had proved impossible to set the British economy on a steady course. Rigidities in the labour market ensured that growth rapidly led to inflation and to trade deficits. Fixed exchange rates exacerbated the difficulties of economic management. In July 1962, Selwyn Lloyd was Chancellor, and he had become a prisoner of Treaury orthodoxy; no-one ever accused him of having a first-class intellect. Macmillan decided that a bolder approach was needed.

At that stage, Reginald Maudling was one of the most impressive younger members of the Cabinet. He seemed to combine flair and stability. Macmillan fixed on him as Chancellor. But he decided on a more general reconstruction, to take place in the autumn, which would bring on new talent. He discussed his plans with Iain Macleod, the party Chairman, and Rab Butler, the then Home Secretary.

That was a mistake. Butler, often garrulous, went to lunch with Lord Rothermere, the proprietor of the Daily Mail, and leaked. That was on July 11th. Not surprisingly, the next day's Mail led with the story. So Macmillan had to move fast.

This helps to explain the decision to sack seven Cabinet ministers. Most of them were time-expired, and most of the replacements were impressive. Maudling and Peter Thorneycroft were promoted within the Cabinet. Enoch Powell, then the Health minister, was given Cabinet rank in the same post. John Boyd-Carpenter, Edward Boyle, Bill Deedes, Keith Joseph, Reginald Manningham-Buller and Michael Noble all joined the Cabinet. With the exception of Manningham-Buller, these were all first-rate appointments.

But the scale of the bloodshed and the general impression of panic aroused widespread derision. The reshuffle was quickly nicknamed the Night of the Long Knives, referring to Hitler's purge of the SA in 1934. In retrospect, a smaller reshuffle would have been wiser. Was it really necessary to replace Lord Kilmuir as Lord Chancellor? Surely John Maclay could have lasted another year as Scottish Secretary? Did Bill Deedes, effectively the information minister, really have to be in the Cabinet?

As it was, Harold Macmillan ended with a stronger government and a diminished reputation. It was a good reshuffle, but bad politics.

In the summer of 1981, Margaret Thatcher was worried. The economy was not responding to her economic reforms. Unemployment was rising rapidly and inflation seemed out of control. There was widespread dissidence, not least in her own Cabinet. From the days of Ted Heath, she had inherited a number of senior figures who had no enthusiasm for her monetarist revolution. Some of them gave the impression that they were waiting for her to fail. So she decided to seize control of her own Cabinet.

She sacked Mark Carlisle, an amiably ineffective Education Secretary, and Christopher Soames, the Leader of the Lords, an unrepentant Heathite. She also dismissed Ian Gilmour, a committed Keynesian, and, ironically, Peter Thorneycroft. In 1958, he had rebelled against Harold Macmillan's economic policies. When she recalled him as Party Chairman in 1975, she was signalling a move in new directions. But Thorneycroft had lost faith in her strategy.

She also displaced Jim Prior, who had been Employment Secretary. She thought that he was not prepared to be tough enough on the trade unions. So he was exiled to Northern Ireland.

The replacements were even more important than the departures. Janet Young took over from Lord Soames. Although Janet was as decent and honourable as anyone in public life, she will mainly be remembered as the only other woman who served in a Thatcher cabinet. But the crucial changes took place in the Commons. Mrs Thatcher promoted Nigel Lawson, Cecil Parkinson and Norman Tebbit. Now, at last, she had a Thatcherite Cabinet

Macmillan's reshuffle deserved a better outcome. Margaret Thatcher's turned out to be the most important reshuffle in British political history. David Cameron's... we shall see.