Later I went looking for a new headlight bulb for the Monster. In typical Halford's style, they didn't have the exact bulb I wanted, but as I needed a replacement fairly urgently, I bought the only one they had, which was a Bike It light. For £3, I can't really complain, but I will be jumping on Ebay this afternoon to hunt down some of those Philips ones. Basically, they give a bike's headlight an orangish glow, which helps distinguish the light on the front of the bike, from the white, or blue lights of the other vehicles on the road. A simple but effective solution to a slight problem.
Looking at the headlight on the Monster, there are two screws on either side, that when undone, release the headlights assembly, allowing very easy access to the back. So, about three mins later, the replacement bulb was in and I was popping the headlight back on. Easy. A put a dab of threadlock on the screws just for good measure. Below you can see a few pics, with a lovely before and after comparison there for good measure.