Prince Charles wants to change British law so that when he accedes the throne he'll be entitled "Defender of Faith," rather than "Defender of the Faith," to reflect Britain's multidenominational society. (Apparently he originally wanted "Defender of the Faiths," but that caused too much controversy.
It would be really interesting to look over the documents and statements surrounding this discussion and see exactly why and how "Defender of the Faiths" was more controversial than "Defender of Faith". My first thought is that simple, indefinite "Faith" can mean whatever the hearer or reader thinks it means, and so Anglicans can go on thinking it means Anglicanism, while "the Faiths" irrevocably and unavoidably acknowledges and validates other faiths. You can keep ignoring religious minorities with the former version, and indeed depending on how you define "faith" you can even argue that the title still doesn't describe them. It's harder (though still not impossible) to do that with the latter version.