British Prime Minister David Cameron says a government review into the Muslim Brotherhood has found that membership of or links to the political group should be considered "a possible indicator of extremism".

The long-delayed review into the organisation, tabled in the British parliament on Thursday, was first commissioned in April 2014 with a remit to examine whether the group put British national security at risk.

"Parts of the Muslim Brotherhood have a highly ambiguous relationship with violent extremism. Both as an ideology and as a network it has been a rite of passage for some individuals and groups who have gone on to engage in violence and terrorism," Cameron said in a statement, describing the group as "deliberately opaque, and habitually secretive".