Tomorrow morning, President Barack Obama will sit down in the White House to receive his daily intelligence briefing from security officials. Thousands of miles away in Kenya, his half-brother will be facing a rather different audience in a Nairobi courtroom.

George Obama, 26, was arrested yesterday for possession of marijuana, after allegedly being caught with a single joint of "bhang" near his home in a Nairobi slum. There was no suggestion that Obama was trying to deal in the drug but, according to Joshua Omokulongolo, the area police chief, rules are rules. "He is not a drug peddler," said Omokulongolo, "But it's illegal, it's a banned substance."

According to CNN, George Obama disputed the charge. "They [the police] took me from my home," he said. "I don't know why they are charging me."

The episode is the latest sad chapter in the life of George Obama, who has largely lived in poverty while his increasingly famous half-brother made his way from Harvard to the Senate and then the White House. While he shares the same father as the US president, he barely knows him and did not attend the inauguration with other Kenyan relatives in Washington last month.

The last of Barack Obama Sr's eight children, George Obama was born less than a year before his father died in a car accident. Four of his half-siblings were born to a Kenyan wife, Kezia, and three - including Barack - to two American women. George's mother Jael is also Kenyan, but he missed out on the opportunities afforded to his half-brothers and sister, most of whom have studied and lived overseas.

In Barack Obama's book, Dreams from my Father, where he recounts his family history, he talks of briefly meeting George at his school in Nairobi in the late Eighties. It was a "painful affair", cut short by a principal who realised that the visitor from America did not have permission from Jael to visit the "handsome round-headed boy with a wary gaze".

By the time Barack visited Kenya in 2006 as a senator, George was living in Huruma, a tough Nairobi slum, and training to become a mechanic.

Last year, during the election campaign, the Italian edition of Vanity Fair claimed to have "found" George Obama, after meeting him at his step-grandmother's home in Kogelo, western Kenya. The report claimed - controversially - that he lived on a dollar a month, and that he was ashamed to be an Obama.

While he is poor and lives in ramshackle accommodation, George is in the same position as well over a million other people who live in Nairobi's slums. Before the US presidential election, he said that he saw no reason why Barack Obama should support him financially; he was content with his life and could provide for himself. That did not stop Jerome Corsi, the right-wing US author of The Obama Nation, from travelling to Kenya in the hope of presenting a $1,000 cheque to George. Fortunately for Corsi, whose stunt was unlikely to have gone down well in Huruma, he was quickly deported.

On 4 November, George was in Kogelo with the extended family to watch his half-brother's triumph. Shortly before the result was announced, he was beaming with pride. "I think my brother is going to be the next president," he said.

Although Kenya is strict about drug possession, there does not appear to be any current police campaign to crack down on usage. The officers who arrested George did not disclose why they searched him, although they are often conducted in the hope of extracting a bribe.