I'm pretty sure stretching your wheels will weaken them.
not sure on the limits but yes you can fail an MOT by having stretched tires!
dam sure u cant, dont think theres anywhere in the mot manual saying you can fail it on it
my mate has 185's on a 9j rim and they were a b**ch to fit
so you cant fail??
i dont want a massive or much of a big strech only a little bit as it is so i should be alright then i suppose