Philp welcomed the public inquiry into the “devastating attack”, because the girls’ families “deserve answers… to ensure this never happens again”.

“There are many questions that remain unanswered about what went wrong,” he said.

“We also need to know who in government knew what and when, as well as why the authorities may have withheld some information from the public.

“As Jonathan Hall, independent reviewer of terrorism legislation, has said in the past being open at an early stage is important to maintaining public confidence.”

Reform UK leader Nigel Farage claimed the handling of the Southport case was “one of the worst cover-ups” he had seen in his lifetime – saying that he had asked questions about whether Rudakubana was known to the authorities but was given “no answer” and had instead been “completely vilified”.

Following the court proceedings, Merseyside Police Chief Constable Serena Kennedy denied there had been any cover-up.

She said: “We have been accused of purposely withholding information – this is absolutely not the case.

“From day one we have been as open as we possibly could and have constantly been in touch with the CPS who have advised us on what information could be released.

“We have wanted to say much more to show we were being open and transparent, but we have been advised throughout that we couldn’t do so as it would risk justice being delivered.”

“We will never know why he did it,” she said, adding: “What we can say is that from all those documents no one ideology was uncovered, and that is why this was not treated as terrorism.”

The BBC has been told that before the attack Rudakubana had been referred to Prevent because of concerns about his general obsession with violence.

In December 2019, Rudakubana – then aged 13 – returned to the school from which he had been expelled and assaulted a pupil with a hockey stick, breaking their wrist.

In the same year he had told the NSPCC’s Childline he was going to take a knife into school because of racial bullying, which breached their threshold for a referral to local authorities.

Jonathan Hall KC, the independent reviewer of terrorism legislation, said the inquiry needed to review Prevent and how the government deals with “people who are obsessed by violence but not necessarily by ideology”.

He told the BBC Radio 4 Today programme: “What I would hope is that someone… is going to look at, ‘how do you pick up these people for whom Prevent wasn’t really designed?’

“In its present format, it needs to change because of the internet – that’s the key factor.”

Speaking outside court on Monday, Ursula Doyle, the CPS prosecutor, said Rudakubana was “a young man with a sickening and sustained interest in death and violence – he’s shown no signs of remorse”.

Matt Jukes, the head of counterterrorism policing, said a thorough investigation will take place now Rudakubana has pleaded guilty.

“The same determination we have shown in the investigation will now be applied to examining how the range of agencies involved with Rudakubana did not come together effectively to identify and deal with the risk he posed,” he said.

Rudakubana is due to be sentenced on Thursday and is expected to be given a life sentence.

However, he cannot be sentenced to a whole-life term for his crimes because he is under the age of 21.