Should a British political leader say this and enact laws on such a basis? Actually, I think not – not in such sweeping terms. If he did, individuals would be unfairly treated, and our nastier fellow-citizens would feel emboldened to persecute and try to drive out Muslims already here. But there are policy ways of addressing the problem – better “civics” in schools, more vigilance about what Islamic charities do, stronger loyalty tests for those arriving, much more study of what is said in mosques and who pays for them, policies which recognise that a Muslim state-funded school or a student Islamic society is, in reality, a much more dangerous proposition than a Christian or Jewish one. David Cameron is thinking in this way when he emphasises the role of non-violent, as well as violent extremism, in poisoning minds.