Shy? I'll give you blunt.
That is the stupidest, most ill-conceived and reactionary idea I've heard in a while. If you want to see Britain implode, make it a country with only a single state run religion. Seems like a civil war was fought over that already. Oh, and the U.S. eventually developed out of that kind of British religious intolerance. There are several major stumbling blocks, the first of which starts with an I and ends with a slam. You want to tell the large number of Muslims in the kingdom they can't practice? Yeah. You would turn London into Prime Target Number 1. Or maybe you were thinking of Islam, in which case I have to say don't forget all those Brits. They may be polite and everything, but historically speaking they are used to long, isolated fights for survival. To paraphrase Eddie Izzard, they'll get the pots and pans and ice cream trucks. Also, did you miss that whole decades long spat in Ireland? Best get ready for round two. And what about your allies? You want to suddenly stop Americans from traveling to Britain, or would you ask us our religion first? Dumb idea, man.