To Auma Obama, who works in children’s services for a council near Reading, he is simply her brother. “I’m proud of him and I want him to do what he wants to do, but it’s scary. Being in the spotlight is not necessarily a good thing,” she said.

Auma married a British man just over 10 years ago. They are now divorced but they have a nine-year-old daughter.

Her brother, 45, shot to fame last month when he announced he was considering standing for president. Although he has been a senator for only two years, Obama wowed Democrats with a speech at the 2004 presidential convention and his book, The Audacity of Hope, is a US bestseller.

Born in Hawaii to a white mother from Kansas and a black father from Kenya, Obama could become the first African-American president of the United States. He did not meet Auma, his half-sister, until his father, also called Barack, died more than 20 years ago.

Auma was born to Obama Sr’s first wife in Kenya, before he left Africa for Hawaii on an overseas scholarship. There he met Barack’s mother and married again. But the marriage did not last and he left his wife and two-year-old son behind when he was admitted to a postgraduate course at Harvard. From there he returned to Kenya.

“I knew about Barack from my dad,” Auma recalled. “We had photographs of him, but he was in America and I was in Kenya. As kids you don’t bother to keep in touch.”

After their father’s death, the young Obama wrote to Auma. The letter shocked her: “Barack had the same handwriting as my dad and the same name. It was eerie.” Obama was eager to learn more about his father. “He felt sad because he had passed away and he hadn’t really known him.” Auma eventually met Obama in Chicago, where he was a community activist.

“I knew at that moment that I loved [Auma] so naturally, so easily and fiercely that later, after she was gone, I would find myself mistrusting that love,” he recalled in his memoir Dreams from My Father.

Auma had not dared to hope they would get on so well: “It was amazing. We had expected it to be difficult but it was easy. We had a very similar outlook on life.”

Auma is wary of politicians. Her father knew many politicians in Kenya, but fell out with President Jomo Kenyatta and was blacklisted. “My dad didn’t suffer fools gladly and you have to be diplomatic. Barack is different. He is able to relate to people. I’m more like my dad. I don’t have Barack’s patience.”

In 1987 she took Obama to their father’s village in Kenya, where he met his grandmother and other members of the family. When they returned last August he received a rock star’s welcome.

Obama will decide whether to stand for president after this week’s mid-term elections. If he has already made up his mind, Auma is not telling: “Barack hasn’t changed. He’s doing what he’s always done. It’s the world that is changing around him.”

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