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There are unconfirmed rumours that a British businessman thought to have been murdered in China was poisoned.

The allegation appears to have come from a report on a Chinese-language website based outside the country.

The Chinese authorities have made no comment on the rumours.

However he died, the death of Neil Heywood has sent shockwaves through China's political establishment.

His death has been linked to the downfall of one of the country's most prominent politicians, Bo Xilai, and has undermined China's planning for a leadership reshuffle later this year.

Potassium cyanide

This is a new twist in a story which has precious few facts.

Boxun, a website based in the United States, claims that the British businessman Neil Heywood was poisoned with potassium cyanide.

That rumour was repeated by people using Chinese micro-blogging sites and has been picked up by some Western newspapers.

Mr Heywood died in the city of Chongqing last November.

The British embassy and the Briton's family were told by the Chinese police that "excessive alcohol" was the cause.

They did not think the death was suspicious and Mr Heywood was cremated a few days after he died. A British diplomat was present.

But when several of Mr Heywood's friends raised their concerns about the death, the British government asked China to re-open the case.

They did, and on Tuesday announced that they now think he was murdered.

Prime suspect

So far, the police have not said publicly how they think Mr Heywood died. It is understood that they have not even told the British government about their findings.

But the authorities have revealed the startling news that the wife of one of the country's most popular politicians is a prime suspect.

Gu Kailai has been detained on suspicion of murder, together with her personal assistant. Her politician husband, Bo Xilai, has been stripped of his positions at the top of the ruling communist party.

The death has undermined the party's planning for a once-in-a-decade reshuffle in the Chinese Communist Party later this year.

Bo Xilai had been tipped for promotion before the latest developments.

The Chinese government has tried to downplay the connection between Mr Heywood's death and the political changes taking place in Beijing.

A commentary piece published by the state-run Xinhua news agency on Sunday said the death is being handled normally and should be treated without "fuss, not to mention excessive interpretation or bias".

"It has nothing to do with a so-called 'political struggle'," it went on.