Could anyone offer some tips on how to sculpt or mold a large piece of cheddar into a knight of the realm. I have tried on a smaller piece but the cheese tends to crumple and doesn't seem sculpt in the way I expect.
Firm cheeses like cheddar can make excellent material for sculpting, which sounds like what you're after. If you really mean sharpening, well... you'll need a very hard cheese, like an aged Parmagianno Reggiano or Romano to get a good sharp edge, and even then it'll require frequent honing to keep the edge in good condition.
In my experience it's possible to carve cheddar, but you need a sharp knife and you need to keep the cheese cold. Depending on your room temperature, you may only be able to work on it for about 15 minutes at a time before you have to put it back in the fridge.
I once managed to sculpt a piece Wensleydale into a clog shape and as mentioned above the best approach is to keep putting the knife back in the fridge every 5 minutes to make it colder. The knife should always be colder than the cheese, that's the secret. Good luck musters.
Unfortunately, I've never had success with Knights of the Realm, have you tried starting off with Viscounts or something simple like that? If you are struggling with room temperature it may be prudent to carve outside in the back garden on a workbench in Scotland.