They have taken advantage of a loophole in the laws against bigamy by going through a “nikah” ceremony at a mosque rather than registering the marriages officially.

Many are avoiding the expense and obligations of divorce, but an estimated 2,000 or more are men who wish to exercise their “right”, according to traditional interpretations of the Koran, to have as many as four wives.

Such relationships, sealed in a Muslim ceremony conducted by an imam, are recognised by Islamic authorities as marriages in the eyes of God. They are, however, invalid under British law, which leaves many “wives” with no rights to their husband’s income, pension, benefits or share of the family home should the relationship break up.

In extreme cases, women brought from abroad, notably from Bangladesh, to marry a British Muslim have been victims of so-called honour killings by their families after being sent home when the relationship has failed.

Senior members of Britain’s Muslim community are taking steps to try to reduce the number of polygamous relationships. Guidelines issued last year by the Muslim Parliament advise against weddings ratified only through Islamic ceremonies.

“No Muslim should seek to contract a marriage without the full protection of the law of the land,” the guidelines state. “Persons most likely to be harmed by avoiding the civil registration would be the wives, who would only then have the status in the UK of unmarried ‘partners’ — a status forbidden in Islam. The children would be illegitimate. No Muslim man should wish to put his spouse or offspring in such a dishonourable position.”

Imams are urged to “have the courage and integrity” to satisfy themselves that prospective grooms are not already married. A marriage contract designed to remind men and women of their obligations and rights in marriage is also being put together by the Muslim Parliament with the UK Shariah Council. It emphasises equality between husbands and wives and, if widely accepted by mosques, should dramatically reduce the number of imams prepared to conduct ceremonies to legitimise polygamous relationships.

Mufti Barkatullah, a judge on the Shariah Council and one of the authors of the contract, said that some mosques had clamped down on polygamy by checking that couples wanting to wed are not already legally married. It is hoped that by reminding women that they are not inferior to their male partner, the contract will reduce the number of women prepared to become second, third or fourth wives.

The Shariah Council, representing mosques and providing guidance on practical and theological issues for Muslims, deals with 600 applications to marry polygamously each year in Britain. The vast majority of these are only technically polygamous. Some are men and women hoping to legitimise a second relationship having separated from their first partners, but without wanting the stigma, cost or effort of getting divorced officially. Others are women seeking rulings that their first marriage was forced and therefore void.

Mufti Barkatullah, a senior imam in Finchley, North London, estimated that there were 3,000 technically polygamous relationships with another 1,000 fitting the traditional idea of a man with many wives.

Dr Ghayasuddin Siddiqui, leader of the Muslim Parliament, said: “I’ve come across one man who has five wives and I would estimate that there are 2,000 men in polygamous marriages in Britain. Of those, 1,000 have multiple wives based here and the other 1,000 have one here and others in different countries. In my view, in this country there are absolutely no reasons why people would have more than one wife.”

Cassandra Balchin, of the feminist pressure group Women Living Under Muslim Laws, said that wives who had been brought from overseas were most at risk. “They can be sent back penniless to their homeland if the marriage breaks down, having to leave their children behind,” she said. “In societies where a woman is regarded as at fault when a marriage fails, she may even be killed by her family.”

The Home Office said: “It remains a criminal offence in the UK for a man to contract a second marriage while he is lawfully married to his first wife.”

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