One of Britain's most high-profile Muslim lawyers has accused established Islamic groups of peddling "myths" about the Government's main anti-extremism policy.
Nazir Afzal backed the controversial Prevent programme, saying it had stopped people including children travelling to Syria, in an interview with the Times.
Mr Afzal, who quit as chief executive of the Association of Police and Crime Commissioners (APCC) following the Manchester terror attack, also criticised the Muslim Council of Britain, saying it was "reluctant" to stand up for British values and the rule of law.
The MCB said it was "dismayed" at Mr Afzal's remarks.
He told the paper: "It (Prevent) has stopped at least 150 people from going to Syria, 50 of them children.
"It's grassroots - it's not about criminalising and it has an impact but it's constantly undermined by myths that urgently need to be challenged."
The Prevent programme aims to intervene early and provide support for those deemed to be at risk of being drawn into violent extremism.
There were around 7,500 referrals to the initiative in 2015/16.
Mr Afzal, who was previously the chief crown prosecutor in the North West, appeared on the BBC's Question Time programme in the wake of the deadly attack on the Ariana Grande concert at Manchester Arena on May 22.
It later emerged that he had resigned after being told it would be inappropriate for him to appear because of the potentially controversial policing issues that could have been raised.
In his interview with the Times he criticised the MCB, saying that at its annual general meeting last year there was "nothing about radicalisation and nothing about the threat of people going to Syria".
He added: "We all have a responsibility to stand up for British values and the rule of law. They always come to the party reluctantly, rather than routinely doing so because it's the right thing."
A MCB spokeswoman said: "If the issue of people travelling to Syria was an issue for him at that time then he could have made the point at the AGM when he spoke (in 2015).
"To raise this now in the aftermath of the Manchester attack is simply opportunistic and disingenuous.
"In addition to our long held opposition to terrorism, since 2014 we have facilitated grassroots conversations to see what Muslim communities themselves should do to help the fight against terrorism."
The council said any criticism of Prevent was in the spirit of enabling the country to tackle the "scourge" of terrorism, the spokeswoman added.