William Hague has asked for a review of Foreign Office procedures amid irritation in Whitehall that British diplomats, consular officials and MI6 officers in China were slow to highlight concerns about the suspicious death of Neil Heywood.

As David Cameron raised British concerns with a senior member of the Chinese politburo, government sources said the foreign secretary was keen to tighten procedures after a three-week delay in informing him about widespread suspicions about Heywood's death.

In the most detailed British statement on the case, the foreign secretary called on the Chinese authorities to ensure that a full investigation was carried out "free from political interference".

Hague issued a written statement to MPs shortly before the prime minister met Li Changchun, the fifth most senior member of the politburo standing committee of the Communist party of China. Cameron offered to assist the Chinese authorities, and Li said he was grateful for the offer, though it is thought highly unlikely that the Chinese will accept.

Hague said Foreign Office officials raised concerns with him about Heywood's death on 7 February, three weeks after a British businessman in China passed on his concerns to Foreign Office officials. Heywood's body was found in a Chongqing hotel room on 15 November last year.

One government source said: "Ministers would not have objected if the system had been a bit snappier in saying this death seems so significantly out of the ordinary. Ministers would not have objected if they had been told a bit more at an earlier date about his death."

Britain believes that Heywood, who had been close to the former Chongqing Communist party chief Bo Xilai, was poisoned on 14 November. Bo's wife, Gu Kailai, and an employee from the family home, Zhang Xiaojun, are in custody on suspicion of murdering Heywood. Bo is under investigation for disciplinary violations and has not been seen since he was dismissed from his post as party secretary in March.

Bo met the Foreign Office minister Jeremy Browne in Chongqing on the morning of 16 November. Chinese officials informed the British consulate general in Chongqing of Heywood's death in a fax, typed in Mandarin, which arrived at lunchtime on 16 November shortly after Browne's meeting with Bo.

Government sources say they are unconcerned that Browne was not alerted to Heywood's death, because 100 British citizens die every day around the world. But there are concerns about the delay in informing Hague about the case after the warning from the British businessman on 18 January.

British diplomats only stepped up their efforts in early February after Wang Lijun, a former Bo ally and local police chief, made a series of allegations about Heywood's death after fleeing to the US consulate in Chengdu.

Hague, who was informed the following day, instructed British officials to demand that the Chinese authorities launch an investigation into the death. Diplomats contacted the Chinese foreign ministry on 15 February. An investigation was eventually announced on 10 April.

In his statement the foreign secretary said: "I welcome the fact that the Chinese authorities have now committed themselves to undertake the investigation into Mr Heywood's death that we sought. 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.

"We will continue to engage with the Chinese authorities on the progress of the investigation and we stand ready to provide any assistance necessary. Foreign and Commonwealth Office [FCO] officials will remain in close touch with Mr Heywood's family as this investigation proceeds."

The prime minister's spokeswoman said before the meeting with Li: "The prime minister will take the opportunity to raise the case of Neil Heywood, welcoming the launch of the Chinese investigation and emphasising that we are keen to address concerns about the suspicious circumstances of his tragic death. We want to see the conclusion of an investigation that observes due process."

Hague's statement gave a detailed chronological account of the events that followed Heywood's death. He said:

• British consular officials in Chongqing were notified of Heywood's death on 16 November by fax from the public security bureau of the Chongqing municipality. "Chinese officials informed our staff that the cause of his death was overconsumption of alcohol."

• Heywood's family informed the Foreign Office on 18 November that they wished to have his body cremated. A Foreign Office official attended the ceremony.

• Foreign Office officials were made aware about suspicions surrounding the official explanation of the cause of death from 18 January.

• Wang Lijun, the former Chongqing vice-mayor and chief of police, made allegations about Heywood's death when he visited the US consulate in Chengdu on 6 February.

• Hague was informed about concerns surrounding the case on 7 February. He asked officials to make urgent representations to the Chinese authorities.

• The deputy head of the British embassy in Beijing met officials from the Chinese foreign ministry on 15 February to raise Britain's concerns. "He informed them of our concerns about Mr Heywood's death and the suspicion that he had been murdered, and conveyed our formal request that the Chinese authorities investigate."

• The British ambassador made the same request on 21 February to the Chinese ministry of foreign affairs vice-minister for Europe. The ambassador repeated the request a week later to the director general for Europe.

• In the absence of a formal response, the Foreign Office's consular director raised the case with a visiting Chinese official on 22 March.

• The Chinese authorities announced an investigation on 10 April.

Reuters reported that Bo initially agreed to a police investigation of his wife's role in Heywood's murder, before changing his mind and demoting his police chief, citing sources with knowledge of police and government information. Its sources said Wang confronted Bo with evidence implicating Gu in the death on 18 January, the same day the Foreign Office says officials became aware of concerns in the British expatriate community.

Bo was furious and ordered Wang out of his office, but then called the police boss back and indicated the inquiry should proceed, the sources said - only to change his mind again three days later and demote Wang.

"Bo Xilai was shocked and outraged, and then later saw what a threat the case was," one said. "So he quickly removed him from the public security bureau three days later."

Although Wang remained as vice-mayor, he was removed from police duties and given another portfolio. The change was announced on 2 February and he fled to Chengdu four days later, exposing the rift and triggering China's biggest political scandal for years.

The agency said on Monday that police believed Heywood was poisoned after threatening to expose Gu's plan to move money abroad. The Reuters source said Wang personally took over the case after several officials refused to sign off on the report.

Others have suggested that the police chief feared he was being investigated over corruption and may have hoped that raising the issue of Gu would ensure Bo protected him.