Some issues that emerged in a recent Guardian article.
If couples do not marry according to UK civil law (and I have seen a fatwa ruling that they need not register their marriage with the British authorities), there may be serious consequences in the event of divorce; in the custody of children (which always goes against the woman); with respect to alimony (a man does not have to pay any, except for the children) and with regard to rights to a share in the family home (which a woman does not have). During the marriage, a man may coerce his wife to have sex, (though wives do not have that right); a husband may confine his wife to their home; if one or the other partner abandons Islam, (the marriage is declared null and void). It is considered wrong to reject polygamy. If a woman wishes to divorce her husband, it is made dependent on obtaining her husband's permission and the agreement of a sharia court. A woman may not marry a non-Muslim and a man may marry only a Jewish or Christian woman. Legal adoption is prohibited, but if a child has been adopted, he or she may not inherit from the adoptive parents. The Leyton-based Islamic Shariah Council has issued rulings including one that forbids a woman of any age to marry without a male "guardian"; another that says a man only has to intend to divorce for it to be valid; one that insists that a polygamous marriage must be maintained even in the UK (Islamic Shariah Council); and another that excuses a man from making alimony payments after divorce.

If Islamic tribunals are to arbitrate according to such antiquated and discriminatory rulings, they condemn British Muslim women to a life as second-class citizens with barely any rights. And if they claim to advise only within the framework of British law, then what are they doing in the first place? The only solution to this scandalous situation is to ban such tribunals entirely and let Muslims, like everybody else in this country, abide by a single code of laws. Sharia courts must be excluded from recognition under the 1996 Arbitration Act if justice for all does not become a farce.

http://www.guardian.co.uk/commentisfree/belief/2009/jun/29/religion-islam-sharia-britain