At least 85 Sharia Courts already exist in the UK, dispensing often illegal advice, according to the left wing Guardian:

Decisions concerning marriages not recognised under English law, polygamy, and disputes regarding children are being made by at least 85 sharia courts, according to the report by the thinktank Civitas. ...

Muslim arbitration tribunal (MTA), a network of sharia courts, has been operating in London, Manchester, Bradford, Birmingham and Nuneaton since 2007 under the 1996 Arbitration Act. These make decisions that are legally binding and can be enforced by the English courts, provided they do not conflict with English law and both parties choose to use them. ...

"The establishment of Muslim Arbitration Tribunals is an important and significant step towards providing the Muslim community with a real opportunity to self determine disputes in accordance with Islamic sacred law," a statement from the organisation said.

But today's report claims that many smaller and often informal courts are making decisions under sharia law beyond their legal remit.

"About two-thirds of Muslim marriages are not being registered under the Marriages Act, which is illegal," said Neil Addison, a barrister specialising in the law on religion. "A woman with such a marriage would have no choice but to go to a sharia tribunal ... But it's not the way arbitration is supposed to work."