Staff at the Government's food watchdog were annoyed by Cadbury's behaviour during the salmonella outbreak this summer that left dozens of people with serious poisoning, according to documents obtained by The Independent.

Minutes of internal meetings at the height of the outbreak show officials at the Food Standards Agency (FSA) suspected the company's products had caused the illness despite Cadbury's claims that its chocolate was "perfectly safe".

The documents, released under Freedom of Information legislation, show that Cadbury could have been more helpful in supplying information about the contamination, which coincided with a sharp rise in cases of a rare strain of salmonella.

Despite being careful to avoid a public attack on Cadbury, the FSA privately considered that Cadbury had posed an "unacceptable" risk to the public.

Cadbury detected salmonella at its Marlbrook plant in Herefordshire on 20 January, according to the documents. But it was only on 19 June, after tests linked the chocolate and the illness, that the company told the FSA about the contamination.

Cadbury took two days to comply with the FSA's request to withdraw the seven infected products, including Dairy Milk bars.

In July, the Health Protection Agency concluded that Cadbury was the likely cause of the outbreak, which may have infected 180 people. Thirty-seven cases of salmonella with the Cadbury strain, SmvdX07, were reported between March and June. Although Cadbury has not accepted liability for the outbreak, its chief executive, Todd Stitzer, said last month that he was "truly sorry" for the contamination and put losses at £20m. The release of the documents is likely to cast further doubt on the FTSE 100 company's conduct in the affair.

The FSA has withheld many records relating to the poisoning because they might prejudice legal action against Cadbury. But the minutes of FSA meetings indicate it was unhappy with Cadbury's response to requests for information that would have helped it deal with the outbreak.

While the infected bars were still on sale, the minutes reveal that, on 19 June, the FSA agreed to e-mail Cadbury, setting out exactly what information it needed and when. But three days later, the company had still not sent key information. Among the documents was Cadbury's risk assessment - the flawed science it used to justify the sale of the chocolate despite the presence of salmonella. Minutes of a meeting at the FSA's headquarters on June 22, entitled "Risk Assessment", said: "The FSA has asked Cadbury for a copy of its risk assessment, but nothing on paper has been produced ... All requests for information have to be reinforced. It was agreed that Cadbury has produced an unacceptable level of risk to public health."

On the day of the recall, another FSA document recorded a phone call from a Cadbury lawyer arguing with the wording of the recall notice. He queried the inclusion of the Montevideo strain, which linked Cadbury more closely with the outbreak and the statement that the infected products were unsafe.

The inquiry was rebuffed, not least because the official noted the chocolate "does not comply with food safety requirements".

When the recall was announced, Cadburysaid it was "purely a precautionary measure" and that the products were safe to eat. On 30 June, 11 days after Cadbury first admitted the contamination, the FSA found salmonella had infected the Marlbrook plant four years earlier.

From outbreak to recall

* 20 January 2006: Cadbury discovers salmonella at a factory in Marlbrook, Herefordshire.

* 19 June: After learning that the strain of salmonella matches that contracted by victims of food poisoning, Cadbury admits the contamination to the Food Standards Agency (FSA).

* 22 June: FSA documents say Cadbury posed an "unacceptable" risk to the public. A minute says: "The FSA has asked for a copy of its risk assessment, but nothing on paper has been produced. All requests for information [to Cadbury] have to be reinforced."

* 23 June: On day of recall, Cadbury's lawyer complains that the FSA has named the strain of salmonella and stated its chocolate does not comply with food safety requirements. The FSA says: "The company had not given info to confirm that anything else but S.Montevideo was present, and in FSA's opinion, food does not comply with food safety requirements."

* 30 June: Documents supplied by Cadbury reveal the same factory was infected with salmonella in April 2002.