One of Scotland Yard's most senior police officers says criticism of the government's Prevent programme is based on "ignorance".
It was set up to stop people being drawn into terrorist activities, but has been labelled "toxic" by critics.
"They don't understand properly how Prevent works," Cdr Dean Haydon told the BBC's Asian Network.
He added that some criticism came from parts of the community that "don't want Prevent to work in the first place".
The programme was set up by Labour in 2003 and its remit was widened by the Conservative-Lib Dem coalition in 2011.