There’s a lot to unpick there.
Just because someone calls for it, doesn’t mean it exists or it will happen. For example, I could go on national TV & say “LCFC should be promoted to the PL regardless of what happens this season”.
There is no Sharia Law in the UK, although as it’s been mentioned a million times here before, there are some areas that have dispute discussions in the same way as the Jewish Beth Din operates (I believe it’s mainly to do with marriages & divorces). Interesting that one gets mentioned more than the other when they effectively operate for the same reasons.
I’m not a fan of religious-based laws generally, so no.
Christian country suggests the vast majority follow Christianity, but if the stats are anything to go by, I don’t believe that’s the case. You’d have to ask a practising or lapsed Christian why they think the religion has been in decline for the last 70-80 years.