Get a grip, vic!
As you will see from the Wiki article, the Church of England (which, after all, is the established church in England of which the reigning monarch is the head) cannot pass legislation. It can offer legislation to Parliament who can then approve it or otherwise.
This is somewhat different to theoldgit's point about Sikhs and crash helmets. Here, a law which applies to everybody else particularly excludes Sikhs because of their religious foibles.
The exemption was a disgrace when the legislation was introduced and is an even bigger disgrace now. Similar exemptions are creeping in by stealth. It is now arguable that a Muslim woman can give evidence in court wearing a full face mask. No other religions are afforded such a privilege. This is divisive nonsense and breeds hostility.
Your contention that the exemption is OK because the only person at risk is the Sikh is somewhat incongruous, Gromit. The only person ever at risk by not wearing a helmet is the rider, whatever his or her religion. So why is it OK for Sikhs to imperil themselves, but not anybody else?
But, I fear, we digress!