Disadvantage to one individual is not enough to support a claim of indirect discrimination. Employers need only accommodate a religious belief (or justify not accommodating it) if their policy disadvantages a group of individuals.
The Court of Appeal has confirmed that a Christian holding a religious belief that she should visibly wear a cross could not claim indirect discrimination, because she failed to show that there was a group of Christians (even a small one) also holding that religious belief. (Eweida v British Airways, CA)
Inevitably it will be easier to show such a disadvantaged group exists where the belief is a mandatory requirement of an established religion rather than just a desire to manifest the religion in a particular way, but the ruling does not go so far as to say that only mandatory requirements of a religion can be protected.
It is also likely to be harder for an employer to justify interfering with a mandatory requirement than a desire.
It has been reported that Ms Eweida will seek leave to appeal to the Supreme Court.