What was in Enoch Powell’s mind when he made his explosive ‘rivers of blood’ speech on immigration 40 years ago this spring? His repetition of wild allegations against immigrants made by his constituents and his apocalyptic warnings of bloody racial conflict ended his front-bench career. Overnight Powell was transformed into a folk-hero for many and a hate-figure for others. Four decades later, the fallout from his outburst is still toxic, as a Tory parliamentary candidate, Nigel Hastilow, discovered to his cost last autumn when he echoed the view sometimes muttered outside polite society and stated that Enoch had been right.

Unlike the Archbishop of Canterbury speaking recently about sharia law, Powell deliberately set out to shock. But what was in his mind when he made his fateful speech in the Midland Hotel (now the Burlington) in Birmingham on the afternoon of Saturday 20 April 1968? Was it ambition, racism, or his duty as an MP to voice the concerns of his Wolverhampton constituents? Or was there something else preying on his mind?

These are the questions I set out to answer in a documentary for BBC Radio 4 in the first of a major new series of programmes recalling the momentous year of 1968. My investigation hears from eye-witnesses to Powell’s speech and the drama surrounding it. With the help of Peter Brooke, the historian, and the Churchill Archives Centre, Cambridge, where Powell’s papers are held, the programme draws on the latest research to trace the real source of the ‘rivers of blood’.

Ambition and Powell’s rivalry with Edward Heath, the then Conservative leader, were important tributaries of his speech. Before making it, Powell confided in his close friend in Wolverhampton, Clem Jones, editor of the Black Country’s Express and Star newspaper. Likening his forthcoming speech to a firework, Powell remarked that whereas the stars of an exploding rocket usually fell back to earth, on this occasion the stars would light up the sky for quite a time.

Immigration was a huge issue in the West Midlands in the 1960s, and although Powell was shadow defence minister, it was quite reasonable that he, as a senior local Tory, should speak about it. But he went to extraordinary lengths to keep the subject of his speech secret from his Tory colleagues, particularly Heath. Powell was to address the West Midlands Conservative Political Centre, but he gave no hint of his chosen subject to the chairman of the meeting, Sir Reginald Eyre, then a Birmingham MP and Tory whip for the area. Although being reticent with colleagues, Powell had tipped off journalists, as Eyre discovered when film crews arrived.

Eyre recalls the audience being ‘stunned’ by Powell’s dire warning that, ‘like the Roman’, he saw ‘the river Tiber foaming with much blood’. As soon as the meeting ended Eyre phoned Willie Whitelaw, then Tory chief whip, to report Powell’s comments and the media interest. Powell soon realised that his life was about to be transformed when he called to collect his daughters from the Joneses and was greeted by Clem’s wife, Marjorie. She was shocked that he had quoted racist language and told him their friendship was over.

Powell’s speech led the evening news bulletins and was splashed across the Sunday papers. On Sunday evening, Heath sacked Powell. Jim, now Lord, Prior, Heath’s parliamentary private secretary, recalls that Heath had no choice, because if he had not sacked Powell, both the shadow home secretary, Quintin Hogg (previously and later Lord Hailsham), and the shadow chancellor, Iain Macleod, would have quit. They were furious with Powell because, ten days earlier, when the shadow Cabinet agreed a policy of measured opposition to the race relations bill, he had said nothing. Simon Heffer, Powell’s biographer, says that by 1968 Heath and Powell were at odds on many fronts — Powell ‘wanted to provoke Heath’ and probably felt that his speech was ‘a chance worth taking’.

Powell’s gamble took a fearful toll on immigrant communities, who had been recruited by employers as a quick fix for Britain’s postwar labour shortage. Bill (later Lord) Morris worked in a Birmingham engineering factory. He recalls that after Powell’s speech, workmates wouldn’t look him in the eye and there was a loss of trust between blacks and whites. Unforgivably, Powell’s speech gave succour to racists. But the charge that he himself was racist cannot be reconciled with his parliamentary onslaught against a Tory government in 1959 for having failed the Africans beaten and murdered at the Hola detention camp in British-ruled Kenya.

A strong current coursing through the ‘rivers of blood’ speech is Powell’s expression of the intense frustration felt among working- and lower-middle-class communities that immigration was changing their towns when they had not been consulted. Powell represented such people, and at Walsall, two months before his Birmingham speech, he compared their position to being ‘trapped or imprisoned, when all [their] efforts to attract attention and assistance bring no response’. Powell’s rhetoric had also become more potent after 1967, when he visited America and saw the devastation wrought by race riots, and following the arrival in Britain of Kenyan Asians fleeing President Kenyatta.

The final clue to the real source of the ‘rivers of blood’ came in Powell’s Walsall speech when he warned against ‘communalism’, describing it as ‘the curse of India’. Powell’s wartime military service had taken him to India in 1943, and there he developed a burning ambition to be viceroy. The word ‘communalism’ often sprang from the lips of British sahibs in justification of the Raj. Peter Brooke’s research finds Powell echoing this imperialist rationale in Delhi in 1945, when he noted that each Indian party was dominated by a communal group — Hindu, Muslim, Sikh, Untouchable and other minorities. Powell concluded that ‘communalism’ ruled out self-government for India in the foreseeable future because individuals would not behave as rational voters or accept majority decisions if they were in a minority.

On returning to civvy street in 1946, Powell imported this thinking into his work at the Conservative parliamentary secretariat, advising against immigration from India because it would undermine Britain’s homogeneous electorate. The following year Attlee’s government pushed ahead with Indian independence. As his beloved India descended into communal violence, Powell received leaked, confidential reports via his contacts, including a former Indian civil servant, Frank Brayne, detailing the bloodshed. At the foot of a report from Lahore dated March 1947, Brayne scrawled, ‘Quem deus vult perdere prius dementat’ — the chilling phrase intoned in translation by Powell in 1968, ‘Those whom the Gods wish to destroy they first make mad’.

Although Powell abandoned imperialism, he never discarded his fear that immigration would introduce communalism, thereby destroying Britain’s homogeneous electorate on which, he believed, its parliamentary system depended. For Powell, India’s bloodbath and America’s race riots confirmed where communalism led. This nightmare was the real source of his ‘rivers of blood’ speech.