The final programme in the series brings the relationship up to the present day. It reveals: the full extent of support given secretly to Britain during the Falklands War - 'you would have been defeated without us', claims the Secretary of the US Navy; Mrs Thatcher 's rage over the invasion of Grenada - 'like Krakatoa', reports someone dining with her that night; and the divisions created by the Tripoli raid - 'the Americans pushed us to the edge on that one' says one Cabinet member. The relationship under Thatcher and Reagan has been based on a shared belief in strong defence. But, David Dimbleby asks, what happens next if America thinks the Soviet threat is receding.

Harold Macmillan was determined to restore relations between Britain and America after the catastrophe of Suez. The launch of Russia's Sputnik was his opportunity: America needed nuclear bases in Europe, and Britain was prepared to offer them. But the atmosphere of goodwill was soured by Vietnam. American Secretary of State Dean Rusk put heavy pressure on Britain to send a token force in support. The British Government refused, to Rusk's dismay. 'When the Russians invade Sussex,' he said to one journalist, 'don't expect us to come and help you.'

Tonight's programme shows how the Cold War gave Britain a new role in the alliance, as an essential forward base for American bombers; but how her own freedom of action was limited - a truth brutally exposed by the Suez crisis of 1956. As the British launched their invasion, President Eisenhower rang Prime Minister Eden. 'I can only presume you have gone out of your mind', he said.

David Dimbleby charts the changing relationship, not only at the top, but among the ordinary men and women who lived and fought together until Hitler had been defeated.

David Dimbleby tells the story of the impassioned, often bitter, debate that raged in the United States over whether America should get involved in another European war. It ended the night the Japanese bombed Pearl Harbor, and Churchill, as he put it, 'slept the sleep of the saved'.

Every week during the 20s, millions of British cinema-goers had a taste of the American dream - 'a form of life far beyond anything we knew'. In the wake of those films, American business pioneers like Ford, Edison and Firestone launched their assault on the Old World. With the lipstick and light bulbs, patent leather shoes and vacuum cleaners, came the salesmen of the commercial revolution. One example of their technique: persuading a widow to sell her husband's gravestone to raise money for the deposit. The film also reveals some of the subterfuges American companies employed to break into lucrative British markets, and take over British firms.

The first episode tells how the Americans were dragged reluctantly into the First World War, of their nightmarish journey across the Atlantic, their welcome in Liverpool - and their disillusion when the war was over. For President Woodrow Wilson , victory had turned sour, but America had started its journey towards world leadership.