The UK government has refused to say whether Sue Gray will record or publish interviews conducted as part of her investigation into the Downing Street parties, sparking fresh fears of a “whitewash”.

The Cabinet Office also refused to answer openDemocracy’s questions on whether a list is being kept of people whom Gray interviews during her probe – or whether such a list would be made public.

The government has repeatedly used the senior civil servant’s investigation as an excuse to avoid answering questions about the scandal. But transparency campaigners have already sounded the alarm about Gray’s suitability because of her history of shielding Number 10 from scrutiny.

Gray’s investigation could spell disaster for Boris Johnson if she finds that he knowingly misled Parliament with his account of alleged parties inside Number 10 during all three UK lockdowns. His former top aide Dominic Cummings claims the PM dismissed fears that one such event, in May 2020, was against the rules.

Asked whether Gray would explain what CCTV footage she had seen, and who she had interviewed, Cabinet Office officials said only that she has been given full access to all the information she wants.

“It would be deeply concerning if those examining alleged wrongdoing in Whitehall failed to keep a paper trail,” said Daniel Bruce, chief executive of Transparency International.

“Any investigator knows maintaining accurate records is critical to prosecuting a successful case. Given potential police interest in the findings of the inquiry, it’s crucial the Cabinet Office confirm this basic fact about the handling of evidence collected.”

The SNP’s Brendan O’Hara told openDemocracy: “If the Cabinet Office expects the public to take what’s reported seriously, this report must not become a Whitehall whitewash.

“Absolute transparency is essential if this report is going to be accepted by the public. Anything less than that and people’s worst fears about the behaviour of this self-serving government will be confirmed.”

The MP added: “The public made great sacrifices in the fight against the virus, all while Boris Johnson and his colleagues held rule-breaking boozy parties at Downing Street. Tory MPs have a duty to put the interests of the country first and remove him from office. They may try and brush these scandals to the side, but the public won't forgive or forget.”

The Cabinet Office was also criticised by Jolyon Maugham, director of the Good Law Project, who has called for police to take over the investigation into Downing Street’s lockdown parties.

“In any judicial determination of whether the prime minister broke the law we would have clarity about the evidence that was taken into account,” he told openDemocracy.

“For an investigation into whether he adhered to the guidance to have credibility, a difficult ask given it's being carried out by a subordinate, I'd expect similar levels of transparency.”

Last week, openDemocracy revealed that Gray had been consulted about the decision to block a journalist’s request for information about the Grenfell Tower fire, in which 72 people died.

In a separate case, she also urged officials to reject a Freedom of Information request, citing the Chilcot Inquiry into the Iraq “ar as an example of how to “releas[e] information in a managed way” instead.

Last week, one transparency campaigner claimed Gray is “not a person that believes in open and full disclosure”.

Jason Evans, who campaigns for justice over the infected blood scandal that killed his father, told openDemocracy: “Personally, I wouldn’t have confidence in that kind of person to lead an investigation or an inquiry.”