A secondary academy is fighting to give preference to children attending primary schools operated by its trust rather than admitting pupils from closer schools, prompting speculation that this could pave the way for a shake-up of academy admissions policies.

Complaints were made to the Office for Schools Adjudicator (OSA) in August about the admissions policy for Rivers Academy in Feltham, west London, after parents and the local authority were concerned it gave preference to pupils from two primary academies within the trust – Oriel and Oak Hill – purely on the grounds they were within the same academy chain.

The adjudicator agreed with the complainants. Her report said: “It is… not sufficient reason to name a school as a feeder school only because it is a member of the same trust.”

She said some pupils would be “unreasonably disadvantaged” by the two trust primaries acting as feeder schools over others with historic and geographic links to Rivers.

But she has now been overruled after a judicial review sought by the academy sponsor, Aspirations Academy Trust. A new adjudicator must now rule again.

Campaigners are worried this could set a precedent as the government forges towards an all-academy system by 2022.

The Fair Admissions Campaign (FAC) said it could lead to “greater manipulation” and “cheating” in policies while OSA’s chief adjudicator Elizabeth Passmore raised similar concerns.

In her annual report, she said schools would not be allowed to name a feeder school simply because of its “type” and “not the active co-operation and links between feeder and receiving school”. However, she did not say what would happen if an academy trust could show its schools were co-operating.

Alan Parker, a former schools adjudicator, also said an increase in trusts with primary and secondary schools could lead to more policy challenge.

Rabbi Dr Jonathan Romain, a FAC steering group member, said: “Through its plans to make all schools academies, the government is expecting all schools to assume control over their own admissions policy and to more readily compete with one another.

“Experience suggests, however, that this will be a recipe for greater manipulation, cheating and error.”

A Department for Education spokesperson said all schools must follow the admissions code and ensure places were allocated fairly.

He added: “Our recent white paper is aimed at empowering parents to hold schools and the system to account. Alongside this, we will also be consulting on amending the mandatory school admissions code.”

A spokesperson for law firm Michelmores, which supported Aspirations’ judicial review, said: “Following receipt of the grounds for judicial review the adjudicator did not resist the claim and agreed to review the decision, which will now be remade.”