A chain of charity shops which predominantly supports Jewish causes has defended its decision to open some of its outlets on Shabbat.

Howard Brecker, chairman of All Aboard, said it had piloted Saturday opening in 10 out of its 18 shops because of “huge pressure” on the sector. He made it clear that no Jewish staff member or volunteer “has or will be requested to work on a Saturday. That is non-negotiable.”

But one of All Aboard’s previous beneficiaries, the United Synagogue, said it would now have to review its relationship with the charity.

One Orthodox woman who recently donated clothes to an All Aboard shop said the Saturday opening “would bother me. As a front for Jewish charities, they should be upholding Shabbat at least. This will change the way I feel about it.”

In 2015, All Aboard gave little more than £12,000 to charities from a turnover of £2.1 million — compared to donations of £160,000 the previous year. Proceeds have gone to a range of Jewish charities as well as general medical causes.

Mr Brecker attributed the drop in 2015 to the introduction of a new warehouse distribution system.

“All charities were informed in advance and all understood,” he explained. But he anticipated that All Aboard — which has given over £2 million to charity in 30 years — would return to “previous donation levels by 2018”.

The charity had had to contend with the general impact of online shopping, he explained. “The charity shop sector is under huge pressure. Not just in terms of items received for sale, but also in respect of sales to customers.”

Many charity shops experienced their busiest trading on Saturdays, he said.

“In the limited number of shops in which we have trialled these new opening hours, we have already seen an upturn in goods deposited with us on Saturdays and an upturn in sales.”

Many Jewish charities, he added, “receive funds from events and initiatives that take place on or over a Shabbat. This, to our mind, is no different.”

But a spokesman for the United Synagogue said: “We will need to have a discussion with All Aboard to confirm what arrangements they have made, as we may not be able to benefit from money they raise if this contravenes halachah [Jewish law].”

All Aboard was founded by Stella Lucas, the wife of a former United Synagogue president.

Jonathan Joseph, chairman of another charity, Langdon, which helps young people with learning disabilities, said: “All Aboard has been exceptionally kind to Langdon both in offering a number of our members paid and unpaid emplolyment and helping us set up our New Chapters enterprise. Langdon sets considerable store by encouraging its members to respect all Jewish holidays and to keep kosher, and would very much encourage all other Jewish organisations to do the same.”

While the All Aboard shop in Golders Green remains closed on Saturday, a sign in the East Finchley branch was advertising its new opening day.

Previously individual shops sorted out items donated by the public but now they are taken to its new warehouse in Watford and then redistributed to the local branches.

Mr Brecker said the early signs of the new system were “encouraging” and had enabled online sales to grow by 1,000 per cent.

Asked whether any staff were on zero contracts, he said that these applied to six out of 90 and were “by their own choice”. It meant “if a shop needs extra help or somebody goes sick, we have staff that are willing to fill in if its suits them.” Staff on zero contracts received holiday pay, he added.

Lionel Kopelowitz, who was president of the Board of Deputies when it loaned the newly-formed All Aboard office space, said: “It’s generally not acceptable for Jewish organisations to open on Shabbat, I don’t approve. There are six other days in the week, aren’t there?”