British Prime Minister David Cameron on Tuesday offered to help China investigate the suspicious death of an English businessman in a case with links to a former Communist Party leader.

Cameron made the offer during a meeting at Downing Street with senior Chinese politburo official Li Changchun as they discussed the probe into the death of Neil Heywood in a Chongqing hotel last November.

Downing Street said in a statement that Cameron "raised the case of Neil Heywood, saying that he welcomed the ongoing investigation and that the UK stood ready to offer any necessary assistance".

Li "assured him that the case was being examined by the judiciary in full accordance with the rule of law," it said.

The Chinese official thanked Cameron for the offer of assistance "and they agreed that both governments would stay in close contact on the issue".

Li is officially number five in China's ruling Communist Party hierarchy and is its propaganda and media czar.

The statement said both parties also discussed deepening bilateral and trade relations while the British premier "raised the issue of cooperation on foreign affairs, specifically on Syria, Iran, North Korea and Burma".

Heywood, 41, was found dead in a hotel room in November, but the case took a dramatic turn last week when the wife of the city's former party leader Bo Xilai was named as a suspect in his alleged murder.

The Briton had reportedly forged close links with Bo, who was removed from the Politburo one week ago at the same time as his wife Gu Kailai was named as a suspect in the case.

A Hong Kong-based website, quoting party sources, alleges that an official in Chongqing admitted to police that he had provided one of Bo's men with potassium cyanide to get rid of Heywood.

Britain's Foreign Office has defended itself over alleged hold-ups in intervening over Heywood's death, which meant that his body was cremated shortly after his death without an autopsy being carried out.

Foreign Secretary William Hague earlier Tuesday said in a written statement to parliament that the Chinese investigation was launched after repeated requests by Britain.

He said the Foreign Office had initially been told that Heywood died of alcohol consumption but that in January it became aware of rumours in the expatriate community that his death was suspicious.

Hague said allegations about Heywood's death were then made by former Chongqing police chief Wang Lijun to US consular officials on February 6 when he fled to the consulate in an apparent panic and reportedly demanded asylum.

He said Britain wanted assurances from China that the investigation was "free from political interference, exposes the truth behind this tragic case, and ensures that justice is done".