We had those assemblies and they even had some vicar hand out bibles for the students although I doubt that kind of thing would be allowed today. We even had Cliff Richards visit our school and he rambled on about religion as well. There is nothing wrong in learning about other religions but that is what RE is about. Religious schools only have an assembly with their religion and not any other religion. It seems the Nishkam people are so inclusive that they do not even know what assembly a religious school should have. You state that parents don't mind the assemblies of other religions, let's be honest here, the average Sikh parent trusts what ever the school does. The only reason my kid is going there is because the Gurdwara could not not be bothered to build a Khalsa secondary school in the primary school so Nishkam is the best option for al least a Sikh education. If there was a Khalsa secondary school nearby there is no way I would send my kid to Niskham instead of the Khalsa Seondary School.
I did my work experience in a catholic school which is on the same road as the Khalsa primary school and they used to have Catholic assemblies every morning with a prayer and the non Catholics had to be in the assembly but didn't have to take part in the prayer.
The R.E lessons were Catholic but the teachers would ask the non Catholic kids to say about their religion too. There were a few Sikh/hindu kids and few Pakistani but that was it, had a lot of polish kids that couldn't speak English.
There was a little church in the School too not sure how often the kids used it though.
The Sikh Primary school on that road is one of the best in the area and the parents are very happy with it, kids learn a lot about Sikhi in that school more than what your average parents can probably teach or know.
Further down the road theres a also a Muslim school which was one of the worst in the area, it had the worst Ofsted report and was full of corruption/money problems, not sure how it's doing now. They learn how to read and write in gurmukhi and know several japji sahib pauris of by heart.
I know a lady whose kids went to the khalsa primary school but she didnt send her kid to the sikh secondary school because she said a lot of parents are saying it's not that good.
Earlier, the Sikh community seeking Korean citizenship was not having their turbans and long beards when taking an identity card and passport photo.