My first reaction was that even if Relate had the 'right' to end his employment maybe they could have worked round his beliefs in arranging his case load.
But then I started wondering what would happen if a married man and women were being counselled by him and it became apparent that homosexual tendancies of one partner was part of the problem. Or a family with a teenager uncertain about their sexuality.

Discrimmination legislation is a good thing (generally) but must be applied with common sense. So if a job has requirement they should come first. This could be discrimination in favour of one religion in some cases.