David Cameron today offered China "any necessary assistance" in its investigation into the suspected murder of British businessman, Neil Heywood.
The Prime Minister raised the case at talks in Downing Street with the Chinese Communist Party propaganda chief Li Changchun amid continued questions over how the 41-year-old came to meet his death in a hotel room.
No 10 said Mr Li, a senior member of the ruling Politburo, gave an assurance that the case was being examined by the judiciary "in full accordance with the rule of law" and had agreed the two governments would stay in close touch on the issue.
"The Prime Minister offered assistance with any aspect of the investigation," a spokeswoman said. "He (Mr Li) made no decision about whether to take up the offer but he thanked the Prime Minister."
Earlier, Foreign Secretary William Hague set out a detailed defence of the Foreign Office's handling of the case, amid complaints by MPs that it took them three months to raise it with the Chinese authorities.
It was reported last week that Gu Kailai, the wife of the former Communist Party boss in the city of Chongqing where Mr Heywood died, had been arrested in connection with the investigation.
Reports from China have claimed Mr Heywood was a friend of the family and that the two fell out after he demanded a higher fee for helping her to move money out of the country.
The old Harrovian was said to have been lured to a hotel in Chongqing last November where he was given a lethal dose of cyanide.
Ms Gu's husband, Bo Xilai - a former rising star in the party - has since been removed from his post and suspended from his seat on the Politburo in a move linked to a power struggle in the Communist Party elite.
In a written statement to MPs, Mr Hague said Mr Heywood had died on November 14 and that his body was discovered in a hotel room the following day.
The British consulate general in Chongqing was notified by fax on November 16, with Chinese officials informing staff the cause of death was "over-consumption of alcohol".
It coincided with a two-day visit to the city by Foreign Office Minister Jeremy Browne, but despite Mr Heywood's prominence in the British expatriate community and the unusual circumstances of his death, he was not informed.
Mr Hague said ministers were not routinely told the deaths of British nationals abroad, but added: "We need to make sure that they are told in in relevant cases and we will review our procedures."
On November 18, Mr Heywood's family - including his Chinese wife - informed consular staff they had decided to have his body cremated. A Foreign Office official attended the ceremony.
It was not until January 18, Mr Hague said, that Foreign Office officials became aware for the first time of rumours circulating among the British expatriate community that his death may have been suspicious.
Further allegations were made on February 6 when Chongqing's former police chief Wang Lijun visited the US consulate in Chengdu after reportedly falling out with Mr Bo, a former ally.
"Prompted by these increasing concerns, FCO officials informed me on February 7 of the case and the circumstances surrounding it," Mr Hague said.
"I immediately instructed them to make urgent representations to the Chinese authorities and to seek an investigation into Mr Heywood's death."
On February 15, "after establishing as much information as possible", the deputy head of mission, Chris Wood, formally asked the Chinese authorities to investigate.
When he received no response, the Ambassador, Sebastian Wood, twice repeated the request to senior Chinese officials while the Foreign Office consular director raised the case with visiting Chinese officials in London.
On April 10, almost two months after the original request, the Chinese finally notified the ambassador that an investigation was under way.
"We now wish to see the conclusion of a full investigation that observes due process, is free from political interference, exposes the truth behind this tragic case, and ensures that justice is done," Mr Hague said.
"We will continue to engage with the Chinese authorities on the progress of the investigation and we stand ready to provide any assistance necessary."