Chief Rabbi Ephraim Mirvis has joined other faith leaders in opposing a move to legalise assisted dying.

Rabbi Mirvis, the Archbishop of Canterbury Justin Welby, and 23 other prominent figures from the Christian, Muslim and Sikh communities expressed concern that possible new legislation would leave the elderly and terminally ill unprotected.

In a letter sent to every MP, the leaders called for a private members bill to be rejected when it is debated in the House of Commons on Friday, over fears that it could legitimise suicide.

Their concern was "rooted in a profoundly human and profoundly sacred calling to care for the most vulnerable in our society".

The bill "has the potential to have a significant impact", putting many more at risk than it would help, they wrote.

"Five hundred thousand elderly people are abused each year, most by family members, often for financial reasons. Many of these would be vulnerable to pressure to end their lives prematurely.

"The best response to individuals' end-of-life concerns lies in ensuring that all receive compassionate, high-quality palliative care and that this is best pursued under current legislation".

The Assisted Dying Bill, put forward by Labour MP Rob Marris, would allow patients judged to have less than six months to live and who had expressed a clear intention to end their lives, to be allowed to do so.

Rabbi Mirvis said the proposed law was misguided and potentially dangerous. He said: "The proposed limits to be built into the draft legislation are all inherently fallible and so are profoundly problematic."

Parliament should give urgent consideration to provision of the best possible palliative care, he believed.

"There is no greater value in Judaism than the sanctity of life … its preservation takes precedence over other commandments and it is not ours to cut short," the chief rabbi said.

Professor Avraham Steinberg,a leading experts on Jewish medical ethics, agreed. "It's a very wrong move to allow assisted suicide. Once you break the taboo of taking life, where do you stop? There can be no safeguards," he said.

The professor, who was visiting the UK from Israel as scholar in residence at Finchley United Synagogue, added: "From a Jewish point of view, commiting suicide is a grave sin. Assisting anyone to commit suicide is a grave sin. It is not allowed under any circumstances."

But Rabbi Jonathan Romain, who chairs a group of faith leaders who support assisted dying, said it was not a mortal sin but a religious option. He said: "We hold that life is precious, but when it becomes unbearable, there is no reason for someone already dying who wishes to relinquish it to be forced to carry on against their will."