This article mentions a dozen reasons why some British women are wearing the niqab, ranging from it being an "an act of faith," to an "act of empowerment," to a practice that gets you good "grades" (I swear it's not my word) that move you to the head of the line of people pushing and shoving to enter Paradise.
I find it interesting that wearing the niqab is presented in the article and by the women interviewed as a personal decision on the part of individual women, who seem to be making that decision in isolation from their husbands, parents, or peers. That is not totally convincing. The Wahhabi mosques and preachers surly play an important role in presenting the niqab as an option for these women. They should be an important part of any investigation of the niqab.