There are as many as 85 sharia courts operating in Britain, according to a new report.
Academic Denis MacEoin, the report's author, said the existence of the courts practising Islamic law could lead to different legal standards being applied to Muslim and non-Muslim citizens.
He said many of the courts operate out of mosques and their rulings are closed off to non-Muslims.
In previous reports it was claimed there were only five sharia courts in the UK, working in London, Manchester, Bradford, Birmingham and Nuneaton.
He said: "This is not a matter of eating halal meat or seeking God's blessing on one's marriage. It is a challenge to what we believe to be the rights and freedoms of the individual, to our concept of a legal system based on what parliament enacts, and to the right of all of us to live in a society as free as possible from ethnic-religious division or communal claims to superiority and a special status that puts them in some respects above the law to which we are all bound."
His report, published by the think-tank Civitas, includes a list of previous sharia judgements which he believes give an indication of the type of ruling being handed down by the courts working in the UK.
Among the examples quoted are laws banning a Muslim woman from marrying a non-Muslim unless he converts to Islam and the removal of a wife's property rights in the event of divorce.
The report states: "Among the rulings ... we find some that advise illegal actions and others that transgress human rights standards as they are applied by British courts."
