Britain faces a “new threat” of terrorism and extreme violence from “loners, misfits, young men in their bedrooms” following the Southport murders, Sir Keir Starmer has warned.

Horrific killings carried out by Axel Rudakubana were “not an isolated ghastly example” but a sign that “fundamental change” is needed to protect the children, said the Prime Minister.

Making the case for new laws and a crackdown on the “tidal wave” of violent material available online, Sir Keir suggested the UK could see a wave of school shootings following the pattern in the US.

And it was revealed that 162 people were referred to the counter-terrorism Prevent programme last year because of “concerns relating to school massacres”.

Sir Keir said: “The tragedy of the Southport killings must be a line in the sand for Britain.”

The Government has already contacted social media firms demanding they take down material that Rudakubana is known to have accessed.

Home Secretary Yvette Cooper said it was “a total disgrace” that Rudakubana was able to buy a knife on Amazon despite having previous convictions.

She described the murders as “one of the most barbaric crimes in our country’s history”

Barrister David Anderson, an independent of the House of Lords, has been appointed to lead a review of Prevent, with Ministers pledging it will ask questions “unburdened by cultural or institutional sensitivities and driven only by the pursuit of justice”.

However Conservatives are calling for it to be upgraded to a statutory inquiry, which would have the power to compel witnesses to give evidence, and say it must look at the government, police and prosecution service response to the murders.

Conservative shadow home secretary Chris Philp said: “We owe it to the memory of those children and their bereaved parents to learn the lessons from this terrible incident and to take steps to make sure it doesn’t happen again.”

The chilling warning that the nation’s children are in danger came after 18-year-old Rudakubana pleaded guilty to the horrific murders of Alice da Silva Aguiar, nine, Bebe King, six, and Elsie Dot Stancombe, seven. Rudakubana killed the girls running amok with a knife at a Taylor Swift-themed dance class last July, where he injured eight other children and two adults.

Rudakubana further pleaded guilty to charges of producing chemical poison ricin and possessing an Al Qaeda training manual, while it has emerged that he was referred to the government’s counter-terrorism Prevent programme three times between 2019 and 2021.

However police investigating the killings said they were not treating them as terror-related and the Prime Minister is now battling claims that the Government or police were involved in a “cover up”. Conservative leader Kemi Badenoch said last night: “There remain serious questions about the transparency of government information at the time of the unrest following these horrific killings.”

Sir Keir confirmed that he knew about the potential terror link during the investigation but insisted “the law of this country” prevented him revealing any information until the trial concluded.

He also suggested that Rudakubana did not fit the usual definition of a terrorist because he was not part of an organised terror group. The Prime Minister said: “My concern in this case is that we have clearly got an example of extreme violence, individualised violence, that we have to protect our children from, our citizens from.

“And it is a new threat. It’s not what we would have usually thought of as terrorism when definitions were drawn up, when guidelines were put in place.”

Warning the UK could see a repeat of school violence that has afflicted America, the Prime Minister said: “I do think it’s new. You’ve seen versions of it in America with some of the mass shootings in schools

“It is not an isolated ghastly example. It is in my view an example of a different kind of threat and that is why I am absolutely so determined that we will rise to that challenge and make sure our law, our response, is capable , appropriate and can deal with that sort of threat.”

Highlighting the need to remove material promoting violence from the Internet, Sir Keir said: “That is not just the laws on terrorism, the framework on terrorism, it is also the laws on what we can access online. We still have rules in place in this country about what you can see at a cinema and yet online you can access no end of material.”

Ms Cooper said she was “deeply disturbed” by the number of cases “involving teenagers drawn into extremism, serious violence and terrorism”.

She revealed: “There has been a three-fold increase in under-18s investigated for involvement in terrorism in just three years.

“162 people were referred to Prevent last year for concerns relating to school massacres.”

And the Home Secretary said she would tackle online knife sales after Rudakubana was “easily able” to buy a knife on Amazon.

She said: “That’s a total disgrace and it must change”.

Mr Philp said: “The inquiry will find out I hope whether mistakes were made and whether the law needs to change.”