We are talking about London, not Britain. We are also not talking about the scale of migration to London but what defines being an indigenous Londoner. I'd also take a note out of your comments regarding Hindus and integration. All ethnic groups have groups within that understand what migrating to a new location brings with it and those that do not or do not care. You can't be 100% that one group understand something better than another
Every minority that moves to a culturally different location, will naturally seek out people that they identify with, regardless of which particular religion or racial group they belong to.
Integration is another term I find almost meaningless in this context.