The Metropolitan Police has asked Downing Street to make sure Sue Gray's report into allegations of lockdown parties makes only "minimal reference" to the events Scotland Yard is investigating.
The intervention could lead to the delay of the anticipated report.
The Met says officers have not asked for the report to be delayed, but it is in contact with the Cabinet Office to make sure the Gray report's publication does noes not lead to "any prejudice to our investigation".
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In a statement, Scotland Yard said: “For the events the Met is investigating, we asked for minimal reference to be made in the Cabinet Office report.
“The Met did not ask for any limitations on other events in the report, or for the report to be delayed, but we have had ongoing contact with the Cabinet Office, including on the content of the report, to avoid any prejudice to our investigation.”
The statement indicates that Ms Gray will either have to make significant changes to her report before publication or delay it until after the police inquiry concludes, says the PA News Agency.
Sources close to the inquiry have previously indicated that she was concerned about the prospect of releasing a report that was shorn of some of its key findings.
Officers have not confirmed how many events they are investigating, but reports have suggested it could be as high as eight.
The official inquiry has been long-awaited but its publication was thrown into disarray on Tuesday when Met Police Commissioner Dame Cressida Dick announced that her officers had opened a criminal investigation.
But some legal figures have questioned why publishing the report would prejudice the police investigation.
Nazir Afzal, a former chief Crown prosecutor for the North West, said on Twitter: “This is absolute nonsense from the Met Police. A purely factual report by Sue Gray cannot possibly prejudice a police investigation.
“They just have to follow the evidence, of which the report will be a part.”
Human rights barrister Adam Wagner, who has spent the pandemic interpreting complex coronavirus laws and explaining them to the public on social media, said on Twitter: “I am not a criminal lawyer so perhaps I am missing something. How would a factual civil service report about events the police is investigating ‘prejudice’ their investigation?”
The anonymous lawyer and author known as The Secret Barrister then added: “I am a criminal lawyer, and I too must be missing something, because there is no reason I can see as to why an independent police criminal investigation would in any way be influenced by, or would seek to influence, a civil service report.”
But Nick Aldworth, a former Metropolitan Police chief superintendent and counter-terrorism national co-ordinator, said the report could prejudice the police investigation “by disclosing the evidence that they will gather and thereby giving the potential defendants an opportunity to conceal or alter evidence”.
Publication of official reports and other inquiries can often be delayed until a police investigation and any subsequent court case or inquest is concluded, typically to avoid the risk of prejudicing a jury if a criminal trial was to take place.
But in this instance, if police investigate under the provisions of the coronavirus regulations then there would be little risk of prejudice as the penalty for breaching lockdown rules is a fixed-penalty notice and it is highly unlikely to result in a prosecution.
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