I meant to say that as McGrath ha indicated, there is no problem about the UK having a Catholic PM. The issue of papal opposition would not be a factor. A PM would live with that just as a catholic US president (eg Kennedy) would have to do. Or as Church of England PMs have had to do when their policies have been criticised by Archbishops of Canterbury.

Blair's difficulty was with the Catholic church. He had been accustomed to partaking of the eucharistic bread, courtesy of an accommodating parish priest, but this was stopped on the advice of the primate, the late Cardinal Basil Hume, on the ground that Blair had not been instructed in the faith. (This emerged from correspondence published after Hume's death.)