The UK Government's controversial anti-terror programme is not doing enough to tackle "non-violent Islamist extremism", a landmark report claims.
The long-delayed review of Prevent - which aims to stop people being radicalised into terrorism - says it must return to its "core mission".
"Prevent must return to its overarching objective: to stop individuals from becoming terrorists or supporting terrorism," it states.
The review adds that it is "correct" for the anti-terror programme to be increasingly concerned about the growing threat from the extreme right.
But it claims: "The facts clearly demonstrate that the most lethal threat in the last 20 years has come from Islamism, and this threat continues."
The review of Prevent was first commissioned in 2019 by Priti Patel and in the time since, several terrorist attacks have "blighted our nation", the report states.
They include the attack on Fishmongers' Hall in central London in November 2019 and the murder of the Tory MP David Amess at his constituency surgery in Southend in October 2021.
The 192-page review states Prevent "is not doing enough to counter non-violent Islamist extremism" and "has a double standard when dealing with the extreme right-wing and Islamism".
Mr Shawcross says it is "clear" Prevent is "out of kilter with the rest of the counter-terrorism system, and the UK terrorism threat picture".
"Islamist extremism represents the primary terrorist threat to this country – consistently accounting for the majority of terrorist attack plots both carried out and thwarted by the intelligence services," his report adds.
It also warns that Prevent is "carrying the weight for mental health services" with some being referred to the scheme "who do not necessarily pose a terrorism risk are being referred to Prevent to access other types of much-needed support".
"This is a serious misallocation of resources and risks diverting attention from the threat itself".
In her own response, the Home Secretary Suella Braverman said Prevent needs "major reform", as she vowed to implement all the review's recommendations.
The Cabinet minister told MPs: "Prevent needs to better understand the threats we face and the ideology underpinning them."
Ms Braverman added: "80% of Counter Terrorism Police network’s live investigations are Islamist. MI5 are clear that Islamist terrorism remains our predominant threat, accounting for 75% of their caseload. Yet only 16% of Prevent referrals in 2021-22 were Islamist.
"Prevent has shown cultural timidity and an institutional hesitancy to tackle Islamism for fear of the charge of ‘Islamophobia’. These are false charges that spread fear and misinformation in communities."
But Amensty International's UK Racial Justice Director Ilyas Nagdee said the review is "riddled with biased thinking, errors, and plain anti-Muslim prejudice", adding: "Frankly, the review has no legitimacy".
The organisation also accused the author of having a "history of biased comments on Muslims and Islam".
Mr Nagdee added: "There's mounting evidence that Prevent has specifically targeted Muslim communities and activists fighting for social justice and a host of crucial international issues - including topics like the climate crisis and the oppression of Palestinians.
"A proper independent review of Prevent should have looked at the host of human rights violations that the programme has led to - but these have largely been passed over in silence."
Labour's Shadow Home Secretary Yvette Cooper accused the Government of a "missed opportunity" to build consensus with the review.
"It has instead been mishandled," she added. "The Home Secretary and the Government has not updated their counter-extremism strategy since 2015."
