Yvette Cooper is said to have been aware of the Southport attacker’s terror manual ‘within hours’

A spokesperson for Number 10 said it was “not correct” to say the government had suppressed facts and that it was the responsibility of the police and the Crown Prosecution Service (CPS) to “speak for their investigations and charging decisions.”

Sir Keir Starmer accused the two Conservative leadership candidates of “undermining the police” in their difficult job with their comments.

The former senior counter-terrorism official said the Home Secretary would have been informed of the alleged discovery of ricin and terror-related material as soon as police discovered it. Failure to do so would be a “serious error” under normal protocols, they said.

“It would go straight to the top and that should happen. I don’t understand why it wouldn’t be reported to the Home Office on the same day they found it. That’s certainly what would happen. You cannot find ricin in a suspect you are already investigating for a triple murder and not tell the Interior Ministry,” she added.

They said it would have been passed on to counter-terrorism police in the North West, who would have informed Matt Jukes, the head of Britain’s counter-terrorism police, who would then have told the Home Office.

Unless it was judged to pose a serious threat to public safety, such information would not necessarily be passed to the Prime Minister, although the former officer believed that in such a high-profile case it would likely have been told to No 10.

However, they said it was right that politicians should not make such information public. “It is a live ongoing police investigation. Charges have been filed, but more charges could follow. It is not for politicians to interfere with justice,” said the former officer.

“It is a matter for the Attorney General and the Director of Public Prosecutions. Justice takes its course. It is not up to politicians to interfere.”