The Government is facing renewed calls to overhaul its controversial Prevent anti-extremism strategy amid warnings that it is fuelling distrust among Muslim communities.
The independent reviewer of terror legislation, David Anderson QC, said some Muslims felt the programme - intended to stop people becoming radicalised - was targeting the practice of Islam itself.
While he acknowledged the fears were exaggerated, he said there needed to be greater openness on how the scheme was operating, with more dialogue with the communities involved, if trust was to be restored.
"There is a strong feeling in Muslim communities that I visit that Prevent is, if not a spying programme, then at least a programme that is targeted on them," he told the BBC Radio 4 Today programme.
"In some cases it is even felt that it is targeted not just at Islamists and terrorism or extremism, but at the practice of Islam - people who pray or wear the veil, for example, are sometimes felt to be under suspicion.
"I am sure those fears are exaggerated - and they are certainly not what the programme is supposed to be about - but the fact is they are very real.
"It is frustrating for me to see a programme, whose ideals are so obviously good, falling down on the delivery to the point where it is not trusted in the community where it principally applies."
His concerns follow criticism of the Prevent programme by leading opposition figures, including shadow home secretary Andy Burnham who is Labour's candidate for mayor of Greater Manchester.
Mr Anderson acknowledged there was a "serious problem" with Islamist extremism and some form of anti-extremism strategy was necessary.
However, he said there should be much greater transparency on the research used by the programme and the results achieved with independent reporting to Parliament and the public on how it was working.
At the same time, he called for better engagement with Muslim communities across the country, saying it was "extraordinary" that there was no dialogue between the Government and the Muslim Council of Britain.
"It (Prevent) may be effective but people need to know that and they need to believe that," he said.
"That means the Government has to be more open about what it is doing and it has to subject itself to some kind of independent scrutiny that can judge whether it is effective or whether it isn't."