A CRACKDOWN on Islamist extremism could turn officers into “thought police,” the copper leading Britain’s Prevent anti-radicalisation programme warned yesterday.

Sir Peter Fahy said that PM David Cameron’s vow to “aggressively” pursue and disrupt extremists trying to spread the “poisonous ideology” of radical Islam could backfire.

The Greater Manchester Police chief constable, who will retire this month, said that the plans could “undermine” the values the government aims to defend, calling into question what it has termed the “British values” of democracy, equality and tolerance.

The PM recently launched new counter-extremism measures.

Among them is a ban on Islamic extremists working with children, putting them under similar restrictions to paedophiles.

There will be bans on radical preachers posting material online and internet firms will work more closely with police to stop extremist material being disseminated.