Can I replace the D bushes on the rear anti-roll bar?
 

I've been told got to buy the whole thing - or can I replace just the D bushes on the rear anti roll bar?

Some people on here have definitely cut off the old and cut into the new to wrap it around the ARB as a fix.

Yes it's possible. The bar doesn't even need to come out but it makes it easier if you happen to be replacing the drop links at the same time. There are two diameters 19 and 21 mm iirc so check that out. The originals are bonded. Mine were worn to the point that one fell of and the other peeled off easy after cutting with an old carving knife. Bit of grease on the knife makes short work of the rubber. The aluminium bush clamp looks like it will never align up but just stay with it and it will go back. Don't expect the same life :)
And you have to split the new ones lengthways along the flat part of the D.