Officially Mk.8 ammo is for machine guns, boat tailed bullet, and it's hotter (by like 100 fps?) than regular Mk.7 ball. Troops were not to to use Mk.8 ammo in their Lee Enfields, except in emergencies as it was stated to cause excessive wear to the bore.
There are varying opinions on this ammo's use for shooting around the Web, I've only ever had a handful of cartridges, which I just put away for the collection. I doubt the 5-6 of them I have would really matter, but IF they really were hard on bores, 150 might not do you much good. Keeping with standard thinking, it may not shoot all that well in your rifle, being made for MG use it could have been made to lower standards.
Got me thinking, how many members here reload their .303 with boat tail match kings? I guarantee I'm not alone in that, and they do work, very well! Oh and with no adverse effect!