Barack Obama’s grandfather was imprisoned and brutally tortured by the British during the violent struggle for Kenyan independence, according to the Kenyan family of the US President-elect.

Hussein Onyango Obama, Mr Obama’s paternal grandfather, became involved in the Kenyan independence movement while working as a cook for a British army officer after the war. He was arrested in 1949 and jailed for two years in a high-security prison where, according to his family, he was subjected to horrific violence to extract information about the growing insurgency.

“The African warders were instructed by the white soldiers to whip him every morning and evening till he confessed,” said Sarah Onyango, Hussein Onyango’s third wife, the woman Mr Obama refers to as “Granny Sarah”.

Mrs Onyango, 87, described how “white soldiers” visited the prison every two or three days to carry out “disciplinary action” on the inmates suspected of subversive activities.

Times Archive, 1952: Politics and terrorism in Kenya

The Mau Mau aims are clear enough: to foster trouble at all levels and by all means

• Archive Topic: The Mau-Mau revolt

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“He said they would sometimes squeeze his testicles with parallel metallic rods. They also pierced his nails and buttocks with a sharp pin, with his hands and legs tied together with his head facing down,” she said The alleged torture was said to have left Mr Onyango permanently scarred, and bitterly antiBritish. “That was the time we realised that the British were actually not friends but, instead, enemies,” Mrs Onyango said. “My husband had worked so diligently for them, only to be arrested and detained.”

Mr Obama refers briefly to his grandfather’s imprisonment in his best-selling memoir, Dreams from My Father, but states that his grandfather was “found innocent” and held only for “more than six months”.

Mr Onyango served with the British Army in Burma during the Second World War and, like many army veterans, he returned to Africa hoping to win greater freedoms from colonial rule. Although a member of the Luo tribe from western Kenya, he sympathised with the Kikuyu Central Association, the organisation leading an independence movement that would evolve into the bloody uprising known as the Mau Mau rebellion.

“He did not like the way British soldiers and colonialists were treating Africans, especially members of the Kikuyu Central Association, who at the time were believed to be secretly taking oaths which included promises to kill the white settlers and colonialists,” Mrs Onyango said.

In his book, Mr Obama implies that his grandfather was not directly involved in the anticolonial agitation, but his grandmother said that her husband had supplied information to the insurgents. “His job as cook to a British army officer made him a useful informer for the secret oathing movement which would later form the Mau Mau rebellion,” she said. The Mau Mau used oaths as part of their initiation ceremony.

Mr Onyango was probably tried in a magistrates’ court on charges of political sedition or membership of a banned organisation, but the records do not survive because all such documentation was routinely destroyed in British colonies after six years.

“To arrest a Luo ex-soldier, who must have been a senior figure in the community, is pretty serious. They must have had some damn good evidence,” said Professor David Anderson, director of the African Studies Centre at the University of Oxford and an authority on the Mau Mau rebellion.

The British responded to the Mau Mau uprising with draconian violence: at least 12,000 rebels were killed, most of them Kikuyu, but some historians believe that the overall death toll may have been more than 50,000. In total, just 32 European settlers were killed.

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