A new move to limit the powers of Islamic sharia courts in the UK has aroused concern over its possible impact on batei din.

A private member's bill introduced by crossbench peer Baroness Cox would make it a criminal offence for religious courts to exceed their legal authority.

According to Simon Calvert, of the Christian Institute, which supports the bill, it would have no adverse impact on rabbinic courts.

"Nothing affects the actions of the Beth Din because the Beth Din is already compliant with the law," he said.

But David Frei, director of the United Synagogue's external and legal services, said: "We are concerned about the potential implications of this bill, which goes much further than existing legislation. We will be monitoring developments closely."

Baroness Cox says that new legislation is needed in order to protect the rights of women in sharia courts.

According to the law, religious courts such as a beth din can act as arbitration tribunals, able to settle civil disputes where the parties agree to accept their rulings.

But Baroness Cox argues that there is "widespread concern" that some Muslim tribunals are going "well beyond their legal remit" by deciding family or criminal cases.

Her bill would make it an offence, punishable by up to five years in prison, for a religious court falsely to claim legal authority by deciding family or criminal cases.

Rabbi Yehuda Brodie, registrar of the Manchester Beth Din, said: "Our arbitration hearings are always carried out within the framework of a legally binding consensual agreement signed by all parties".

The Beth Din, he said, "cannot and does not operate, without both parties subjecting themselves willingly to its jurisdiction". It recognised that it had "no jurisdiction" in criminal cases, he explained. While the Beth Din mediated in divorce cases, the parties were advised that "any agreement reached consensually" would have to be approved by a secular court.