Well, since I had a trip to Screwfix already lined up I thought I would pick up some of the heavy-duty degreaser as mentioned by a couple of you. It worked shockingly well, and the years of gunge just seemed to fall away from the cookerhood meshes. Interested to see what this wonderous product contained I thought I'd check the label. It was then that I discovered that one is supposed to dilute this product with water in the ratio of about 1:5. No wonder it was good!
Subsequent to this, I thought I would try the washing powder and hot water on some gunged up grinder parts. This proved to be shockingly effective too! In addition to being water soluble (like the above) this makes nice and familiar smells, enabling one to do horrendous tasks in the domestic environment and get away with it 
After years of messing around with Gunk, paraffin, acetones and various other noxious solvents in the corner of my garage, the above two products are a godsend. Thanks for your ideas and suggestions.
G.