Is my Frozen solid Lamb ok to roast I am asking for food safety reasons
In general, roasting it from frozen to properly cooked in the middle won't cause any food safety issues. It's former frozen-ness and the speed of defrosting won't mean that it grows more bacteria.

The problem is, at oven temperatures, by the time the centre of a large roast is thawed (never mind cooked) the outside will be overdone by anyone's standards. It's one thing to braise meat for a long time, it's another thing to over roast it for a long time. If you go by the done-ness of the outside, you'll take it out while the inside is still undercooked, even raw or still frozen. And that will potentially be a food safety issue.

That's why you should defrost large pieces of meat before you roast them.

If your concern is whether meat that has been frozen for two years is still safe to eat, The consensus is that meat stays safe to eat indefinitely while frozen. It may been freezer burned (especially in a frost free freezer) or not taste as nice as it would have after a few months. I wouldn't use it for a critical meal, family celebration or the like, but thaw it and look at it. If it looks dried out and white on the surface, perhaps cut that part off. Then cook it and try it. If it's awful, throw it out and order a pizza. I wouldn't throw it out in advance just because of the length of time. Being double wrapped may well have protected it.