The average Muslim individual [in the UK] clearly appears to be more attached to her/his culture of origin. Indeed, regardless of the dimension of identity considered, the percentage of Muslims having an intense religious identity is roughly twice as much as that of non-Muslims. A greater resistance to cultural integration is also signaled by the percentage of Muslims speaking English at home or with friends, always significantly lower than those of non-Muslims. Finally, Muslims have almost twice the probability of having a marriage arranged by their parents than non-Muslims, also a sign of attachment to cultural and religious traditions.This is not surprising since (at least) two of the largest Muslim groups in the UK -- Pakistanis and Bangladeshis -- practice (to quite high degrees) consanguineous marriage. [See consang.net's Global Prevalence of Consanguinity map and tables.]
Importantly, the stronger resistance to integration, which our data documents for Muslims immigrants, can hardly be explained by a difference in the time spent in the UK since it is (on average) not statistically different between Muslims and non-Muslims.
This means that the members of these populations are MORE related to one another than are the other members of the greater UK population -- the native English, for example (see coefficient of relationship). Because of this, these Muslim groups in the UK are bound to be MORE "allied" to each other than to the other members of UK society.
In addition, these Muslims will feel and be MORE allied to each other than the members of OTHER sub-populations in UK society might feel and be toward themselves. Muslim groups in the UK simply have more invested in each other genetically speaking than would, say, Polish or Japanese immigrants, groups which practice very little consanguineous marriage. Muslim immigrants will have little incentive to assimilate and every incentive to remain loyal to one another. Biologically this makes the most sense for them (see kin selection).
Finally, it is not strange that even those Muslims who are raised in the UK feel little desire to assimilate. They are no different from their parents in that they, too, are MORE related to the members of their families than are people who do not practice consanguineous marriage.