David Cameron today launched a fierce attack on what he called "state multiculturalism", claiming that it undermined community relations.

"State multiculturalism is a wrong-headed doctrine that has had disastrous results. It has fostered difference between communities," the Conservative leader said in a speech.

"And it has stopped us from strengthening our collective identity. Indeed, it has deliberately weakened it."

Cameron defined "state multiculturalism" as "the idea that we should respect different cultures within Britain to the point of allowing them – indeed encouraging them – to live separate lives, apart from each other and apart from the mainstream."

Speaking at a debate hosted by the Equality and Human Rights Commission, Cameron also:

 criticised the apparent suggestion from the Archbishop of Canterbury for the extension of sharia law into the UK

 claimed that "state multiculturalism" was leading to schoolgirls in Bradford disappearing from school and being forced into marriage

 committed the Tories to promoting integration

Cameron said that in the voluntary sector "state multiculturalism" had involved "granting financial aid for artistic and other projects purely on account of ethnic background – with various groups, purporting to represent various minorities, competing for money against each other."

In public services, it meant "not just essential information, but all information, endlessly translated into numerous languages, to cater for numerous people, who can then continue to go about their daily lives without ever having to learn English.

"More generally, it means treating groups of people as monolithic blocks rather than individual citizens."

Cameron said that his generation did not have the hang-ups of the past and that "people today don't worry that criticising multiculturalism is coded racism".

"Multiculturalism was manipulated to entrench the right to difference – which is a divisive concept. What we need is the right to equal treatment despite difference."

Cameron said that he had "tried in good faith" to understand what the archbishop, Rowan Williams, had meant in his recent lecture about sharia and British law.

If Williams meant that different communities should have different laws, then that would be "dangerous and illiberal", the Tory leader said.

The introduction of sharia law for Muslims would be "the logical endpoint of the now discredited doctrine of state multiculturalism", he said.

He went on: "It would alienate other communities who would resent this preferential treatment. It would provide succour to the separatists who want to isolate and divide communities from the mainstream.

"And it would – crucially – weaken, destabilise and demoralise those Muslims who embrace liberal values and desperately want to integrate fully in British society."

Cameron said that "state multiculturalism" led to people accepting different cultural behaviour, even if it contravened human rights.

"Take forced marriages. In Bradford, where I was last week, schoolgirls under the age of sixteen have simply disappeared from school. Nobody knows where they are.

"And, until recently, there was little investigation – despite the fact that it is likely that they may have been drugged, imprisoned, kidnapped and forced into an unwanted marriage on the other side of the world."

Cameron said that over the coming months he would be unveiling policies designed to "oppose the forces of separation in favour of community".

One idea was for children to have more school exchanges, so they could meet children from different backgrounds.