Pretty sure creating such a unofficial fatwa would be a crime in our own courts who have the power to do something about it.
Although lets test the theory;
I do not believe in the afterlife, nor do I believe in Muhammad, I regularly consume alcohol, gamble and am alone with non blood members of the opposite sex.
Bring it on draggers.
No muslim I've ever met has taken offense at my apparent blasphemy.
Yeah after hearing this if I saw an Irish guy with a bomb it wouldn't matter. Its only when they utter a certain phrase I get worried.
It would be a crime but it wouldn't stop someone taking matters into their own hands for saying Mohammed was a [insert true comments here] and then being attacked.
Try going and saying it in a few select neighborhoods... By Finsbury Park mosque for instance