"In a sample of Pakistanis, first-cousin couples accounted for around 60 percent of all marriages. In a sample of Indians, first-cousin couples accounted for one-third of the marriages, and uncle-niece couples accounted for one-fifth."

I think that it is important to point out that many of these cousin marriages by Pakistanis are the result of the Muslim kinship structure, where marriages to family members strengthen clan ties and guarantee that wealth will stay within families (since dowries are paid by the bride's family). The real downside to this is the fact that most of these marriages are arranged and obligatory, forcing young girls into incestuous relationships against their will. If they refuse the price can be great (honor killings).

Great Britain is considering the issue not just because immigrants want to practice their traditions, but because cousin marriages are another reason why Muslim immigrants so often fail to assimilate. If British officials are smart, they will outlaw cousin marriages so as to facilitate assimilation, avoid health risks to children, and most importantly protect women who would be forced into such arrangements.