I've just come across your message regarding your grandfather's service and notice that he served on both HMS Collingwood and HMS Victory.
My father was on both those ships (and a few others).I can't seem to find much out although I have lots of his war papers and discharge papers.He never spoke much about the war but I know that he was on two ships that were torpedoed and also was in North Africa and then through Sicily and Southern Italy.
All I have found out so far is that HMS Collingwood was a training ship.
Have you found any sites that may give more information? Would love to know how you are getting on with your search.