The UK was late to recognise the need to tackle the extremist views behind terrorism, the foreign secretary says.
Philip Hammond also said there had been a reluctance to "recognise the link between non-violent extremism and violent extremism" in the past.
He said the importance of tackling all forms of extremism was now realised.
Addressing a security summit in Bahrain, Mr Hammond described countering Islamist extremism as "the great challenge of our time".
In the speech, in Manama, he said: "We in Britain, have recognised - perhaps later than we should have - that to prevail in that struggle, we have to tackle all forms of extremism, not just violent extremism."
He added: "For decades we have clung to a false distinction between the two.
"We have tolerated - in fact we've even celebrated in the name of multiculturalism - ideas, behaviours and institutions that have encouraged separateness of identity and intolerance of difference. [BBC] Read more
