Ofsted staff were forced to abandon their inspection of a Muslim primary school in Luton on Thursday after being confronted by parents angry that their children as young as nine had been questioned in private about their attitudes to homosexuality.

The inspectors, including a senior employee, cut short their review of the Olive Tree primary school, an independent Muslim faith school, after the group of parents said they would withdraw their children from the school as long as the inspectors remained.

Ghulam Shah, a parent of one of the children interviewed by the Ofsted inspectors, said his 10-year-old son was upset by the way the questioning was carried out, and that as a parent he was concerned he had not been told the inspectors would be discussing sex with his children.

"He was sat with a male adult who looked him in the eye and said, 'What do you know about gays?' What that made him do, it made him panic, and he said 'I don't want to continue this conversation,' because he felt scared, intimidated," said Shah. "It's horrible for a child to be in a room with somebody they've never met before, who's not with a teacher and not with a parent."

A spokesman for Ofsted said: "We can confirm that inspectors withdrew from the second day of an inspection in Luton. However, sufficient evidence was gathered to complete the inspection."

Ofsted inspectors were left to their own discretion regarding the nature of questions about sexuality posed to different age groups, the spokesman said.

Shah said his son told him about the conversation with the inspectors after he picked him up from school on Wednesday.

"He said, Dad, when they took us to the side room, they said 'Do you guys know what gay means?'. My son said, yes, I do know what it means, what's that got to do with our education? They said, 'Are you exposed to it in any way, good or bad, does the school teach you anything about it? My son replied, no, the school has not taught us anything about it but I have heard of the word and I'd rather not have this conversation with you at all."

Shah said the inspector told his son not to be offended, telling him: "It's just a part of the law we have to ask you."

The questioning into attitudes to homosexuality follows reports that Ofsted inspectors repeatedly asked similar questions of Muslim pupils during the investigation into Birmingham schools over the alleged Islamist plot known as Trojan Horse.

But Ofsted said that questions about homosexuality were not restricted to Muslim or predominantly Muslim schools. "As part of any school inspection, inspectors will ask pupils about the effectiveness of the school's actions to prevent and tackle discriminatory and derogatory language – this includes homophobic and racist language," a spokesman said.

Olive Tree primary is an independent primary in the Biscot area of Luton, run by a charity. Those independent schools in England that do not come under the Independent Schools Council are inspected by Ofsted, under standards set by the Department for Education. Those standards include a requirement that schools have a duty to teach pupils tolerance of different groups within society.

The inspectors questioned the group of nine and 10-year-olds on Wednesday, and then met more than 20 parents who attended a scheduled meeting on Thursday morning as part of the inspection. TAt the meeting the parents raised the appropriateness of the questioning, and after discussion between the inspectors, parents and school, the inspectors opted to withdraw, ending the inspection a day early.

Farasat Latif, who is the chair of the trust that runs the school and a parent whose children attend it, said the meeting was largely amicable.

"One of the parents said to them, and all of us agreed, this is a safeguarding issue, we are not comfortable about adults speaking to our children about issues of sexuality. Therefore either you stop the inspection now or we pull our kids out, and they're in the middle of Sats.

"When they realised we were serious about that, they left," Latif said. "This is about sexualising young children."

The inspectors also asked the children if they had seen anything on the news about terrorism that they had discussed in class.

Shah said the inspectors – when they were made aware of the parents' feelings – did apologise for the manner of questioning: "They apologised three times, we should maybe have used an alternative route, maybe asked the head master, maybe asked the teacher or the parents to be present. But [they said] we can't apologise for the law and what we've been sent out to do," he said.