Moslems have a monoculture all ready to roll!
The reason that immigrants do not adopt English culture is because there is nothing to take root in.
The arid secularism of Britain is a vast, empty wasteland. Only a tiny percent of British go to church every week, and most of them are very old. The young worship the bottle and vacations in Spain.
No wonder the immigrants in the United Kingdom find more sustenance in sharia law and radical terrorism.
Why I say it is too late is mainly because Cameron himself is still confused, as evidenced by the last two paragraphs of his speech.
Cameron still believes that these uprooted heathens from various parts of the globe can still share a common British identity, they can't.
They can however share no identity, but that wouldn't be very British.
Cameron still thinks that Democracy and Islam can coexist, they can't.
All of Western civilization will eventually have to choose, and it will either be "The will of the nation" or "The will of Allah"