At least 85 Islamic sharia courts are operating in Britain, a study claimed yesterday.
The astonishing figure is 17 times higher than previously accepted.
The tribunals, working mainly from mosques, settle financial and family disputes according to religious principles. They lay down judgments which can be given full legal status if approved in national law courts.
Disputes: Islamic leaders rule on disagreements
However, they operate behind doors that are closed to independent observers and their decisions are likely to be unfair to women and backed by intimidation, a report by independent think-tank Civitas said.
Commentators on the influence of sharia law often count only the five courts in London, Manchester, Bradford, Birmingham and Nuneaton that are run by the Muslim Arbitration Tribunal, a body whose rulings are enforced through the state courts under the 1996 Arbitration Act.
But the study by academic and Islamic specialist Denis MacEoin estimates there are at least 85 working tribunals.
The spread of sharia law has become increasingly controversial since its role was backed last year by Archbishop of Canterbury Dr Rowan Williams and Lord Phillips, the Lord Chief Justice who stepped down last October.
Dr Williams said a recognised role for sharia law seemed 'unavoidable' and Lord Phillips said there was no reason why decisions made on sharia principles should not be recognised by the national courts.
But the Civitas report said the principles on which sharia courts work are indicated by the fatwas - religious decrees - set out on websites run by British mosques.
The Archbishop of Canterbury Dr Rowan WilliamsControversial comments: Dr Rowan Williams said a recognised role for sharia law seemed 'unavoidable'
Mr MacEoin said: 'Among the rulings we find some that advise illegal actions and others that transgress human rights standards as applied by British courts.'
Examples set out in his study include a ruling that no Muslim woman may marry a non-Muslim man unless he converts to Islam and that any children of a woman who does should be taken from her until she marries a Muslim.
Further rulings, according to the report, approve polygamous marriage and enforce a woman's duty to have sex with her husband on his demand.
The report added: 'The fact that so many sharia rulings in Britain relate to cases concerning divorce and custody of children is of particular concern, as women are not equal in sharia law, and sharia contains no specific commitment to the best interests of the child that is fundamental to family law in the UK.
'Under sharia, a male child belongs to the father after the age of seven, regardless of circumstances.'
It said: 'Sharia courts operating in Britain may be handing down rulings that are inappropriate to this country because they are linked to elements in Islamic law that are seriously out of step with trends in Western legislation.'
The study pointed out that the House of Lords ruled in a child custody case last year that the sharia rules on the matter were 'arbitrary and discriminatory'.
And a 2003 judgment of the European Court of Human Rights in Strasbourg said it was 'difficult to declare one's respect for democracy and human rights while at the same time supporting a regime based on sharia, which clearly diverges from Convention values.'
However last year Justice Minister Bridget Prentice told MPs that 'if, in a family dispute ...the parties to a judgment in a sharia council wish to have this recognised by English authorities, they are at liberty to draft a consent order embodying the terms of the agreement and submit it to an English court.
'This allows judges to scrutinise it to ensure it complies with English legal tenets.'
Decisions from sharia tribunals can be presented to a family court judge for approval with no more detail than is necessary to complete a two page
form. The sharia courts in the Muslim Arbitration Tribunal are recognised as courts under the Arbitration Act. This law, which covers Jewish Beth Din courts, gives legal powers to a tribunal if all parties involved accept its authority.
Its director Dr David Green said: 'The reality is that for many Muslims, sharia courts are in practice part of an institutionalised atmosphere of intimidation, backed by the ultimate sanction of a death threat.'
The Muslim Council in Britain condemned the study for ' stirring up hatred'.
A spokesman said: 'Sharia councils are perfectly legitimate. There is no evidence they are intimidating or discriminatory against women. The system is purely voluntary so if people don't like it they can go elsewhere.'
Patrick Mercer, Tory MP for Newark and chairman of the Commons counter-terrorism sub committee, said: 'We have an established law of the land and a judiciary. Anything that operates otside that system must be viewed with great caution.
'If crimes are going unreported to police, this will erode the authority of those who have to enforce our law. In a sovereign state there must be one law, and one law only.'
Philip Davies, Tory MP for Shipley, said: 'Everyone should be deeply concerned about the extent of these courts.
'They do entrench division in society, and do nothing to entrench integration or community cohesion. It leads to a segregated society.
'There should be one law, and that should be British law. We can't have a situation where people can choose which system of law they follow and which they do not.
'We can't have a situation where people choose the system of law which they feel gives them the best outcome. Everyone should equal under one law.'
Veteran Tory Lord Tebbit provoked anger among Muslims earlier this month by comparing Islamic sharia courts to gangsters.
He likened the tribunals to the 'system of arbitration of disputes that was run by the Kray brothers'.
Lord Tebbit told the Lords: 'Are you not aware that there is extreme pressure put upon vulnerable women to go through a form of arbitration that results in them being virtually precluded from access to British law?'
Warning that women could be shut out from the protection of the law, he asked Justice Minister Lord Bach: 'That is a difficult matter, I know, but how do you think we can help those who are put in that position?'
