Immanuel College has emailed parents to warn them that pupils must have a supervised kosher bar or batmitzvah party in accordance with school rules.

The independent Jewish secondary school reminded parents of year seven and eight pupils that they signed a contract agreeing to the schools policy on the issue, when their children joined.

The JC understands that Immanuel contacted parents amid rumours of a recent breach of the policy, although the school would not confirm this.

Martin Blain, clerk to the governors, told the JC: "If a child had a non-kosher bar- or batmitzvah, in theory they could be asked to leave, in the same way we might ask a child to leave if they did not pay their fees."

In the email sent on September 29, Rabbi David Riffkin, the deputy head, wrote: "All functions must be catered by a fully registered caterer from one of the following four Orthodox Kashrut Authorities only."

A child could in theory be asked to leave

He listed KLBD London Bet Din, SKA Sephardi Bet Din, KF Federation of Synagogues, and Kedassia as acceptable caterers.

Mr Blain said the school's policy had been "a long-standing requirement for parents for as long as I've been with the school."

He added: "We are an Orthodox school at the end of the day. It is why children come here and it is supposed to promote inclusion. We do it so that no child is excluded. If a parent threw a non-kosher party many of the pupils would be unable to attend."

Mr Blain said he was unable to confirm whether there was any case of a parent from the £16,000-a-year school - which has approximately 640 pupils - arranging a non-kosher simchah.

"It would be a private matter between the school and that parent," he said.

In the email, parents were also advised of the appropriate etiquette when inviting other pupils to such celebrations.

Rabbi Riffkin wrote: "We are happy to distribute invitations at school only if everyone from the year group has been invited, or all the boys/girls if appropriate."

He warned against not inviting only two or three classmates, calling the decision to select the majority but leave a few out, as "very harsh".

He also told parents a special assembly had been given to year seven and eight pupils - aged from 11-13 - on how to behave, including how to dress appropriately.

Mr Blain said: "This should not come as a surprise to anyone. It is normal behaviour from a school and we expect certain things from parents and pupils in the same way they expect to get a great education from us."