Non-Catholic children may be rejected from their sibling’s school after governors agreed to give Catholic families top priority.

Sacred Heart Primary School, in St Mark’s Road, Teddington, told non-Catholic parents their younger children may not be accepted in the future because of an obligation to prioritise by faith when it is oversubscribed.

The rule is contained in a Diocesan Trust Deed, in which the school said there was no scope for change.

Most other schools give priority to siblings of existing students regardless of faith and spare parents the difficulty of having children at different schools.

Parents and Richmond Inclusive Schools Campaign (Risc) have called on Sacred Heart to reconsider their admissions policy after it accepted a one-off bulge class of an additional 30 pupils, including non-Catholic children.

Helen Clark, a Risc spokeswoman said when a Church of England primary school in Camden was faced with a similar issue it agreed to change its admissions policy.

She said: “We hope Sacred Heart’s governors and the Catholic diocese understand the serious issues faced by local parents and will also change their admission policy.

“We will do what we can to support these parents, but surely no parent should be put in this situation in the first place.”

One parent, whose son is in the bulge class, said: “Our son is really happy at the school, and it seems terribly unfair that they may refuse a place to his little brother.

“The council offered us a place originally without warning us about this rule, and now they are saying we will have to apply for a place for our other child and simply hope it will be OK, or move our older son to another school.”

A Richmond Council spokesman said parents were advised that there could be difficulties in securing a place for their younger children and were made familiar with the school’s oversubscription criteria.

The spokesman said: “The school’s admissions criteria do give the governing body discretion to give priority to any applicant under the ‘exceptional circumstances’ criterion if they feel that the particular circumstances of an individual case would justify it.”

The Accord Coalition campaigns to end religious discrimination in schools and is taking the case to the Catholic Archdiocese of Westminster to reconsider its guidance to schools.

Chairman of the Accord Coalition, Rabbi Dr Jonathan Romain MBE, said: “Schools’ conduct should be exemplary, and no state-funded schools should be discriminating on the grounds of religion.

“The blinkered pursuit by religiously selective schools to serve their own, rather than the wider community, and in this case, the families of children at the school, brings into question whether they are fulfilling the social contract that people might reasonably expect of them.

“A humane, and also a religious response would be to find room for siblings of existing children and not to use religious discrimination to split families.

“That does not sit well with the values of most faiths.”