An NHS trust has been criticised for arguing that the family of a seriously ill five-year-old girl are incapable of acting in her best interests because of their Islamic religious beliefs.

The parents of Tafida Raqeeb, who suffered a traumatic brain injury in February and is on a life-support machine, want to fly her to Italy for treatment against the judgment of doctors at the Royal London hospital.

The medics believe it would be in her best interests for life support to be withdrawn and her fate is due to be determined at a five-day hearing at the high court, central London, next week.

Before those proceedings, Barts NHS trust, which runs the hospital, made an application on Thursday for one of Tafida’s female relatives to be removed as her “litigation friend”, a child’s representative in court.

It made its submissions after Tafida’s mother, Shelina Begum, obtained a fatwa – a ruling in Islamic law – from the Islamic Council of Europe, which concluded that it would be a “great sin” and “absolutely impermissible” for the parents or anyone else to consent to the removal of life support.

In written submissions, Katie Gollop QC, acting for Barts, said: “The trust submits that particularly in light of the fatwa, no member of the family is suitable to act as litigation friend.”

She continued: “It is not possible for the family to be open-minded about the fact that a best interests decision made by the [high court’s] family division is, or may be, in Tafida’s best interests.”

In response, David Lock QC, acting for Begum and Tafida’s father, Mohammed Raqeeb, told the court: “However you dress it up, that’s an outrageous statement for a public body to make.”

In his own written submissions, Lock said: “The logic of the trust’s position is thus that anyone who holds the Islamic faith should, by virtue of adherence to that faith, be debarred from being a litigation friend for Tafida.

“Removing the LF [litigation friend] on the sole ground that she holds to the tenets of a major religion and therefore, as a result of her religious convictions, cannot be anticipated to act in a way that reflects the child’s interests is not only highly offensive but would also be unlawful.”

Gollop said it was unfair to suggest the application was discriminatory and rubbished the idea the trust was suggesting no Muslim could be a litigation friend.

The judge, Alistair MacDonald QC, rejected the trust’s application, meaning the female relative, who cannot be named under reporting restrictions, can act as Tafida’s litigation friend next week.

Begum, who was in court to hear the arguments, said afterwards that the application was unnecessary and that it was deeply distressing to have to leave her daughter’s bedside to attend Thursday’s hearing.

Tafida has been in hospital since 9 February after suffering an arteriovenous malformation, a tangle of blood vessels with abnormal connections between arteries and veins.

Her parents say she is not brain dead and has shown gradual but encouraging signs of recovery, including in her breathing. Doctors at the Gaslini Children’s hospital in Genoa, Italy, are willing to treat the “kind, beautiful and bubbly little girl”.

Acknowledging the emotions involved in the case, MacDonald urged the lawyers to ensure they “keep the temperature down” during next week’s hearing.