I had bought a few downlight fittings from ebay so I thought I might as well put a couple of these up. I had left an opening in the ceiling cloud which currently accommodates a temporary bulkhead light. The idea is to fill this with a small piece of plasterboard with a couple of openings for two downlights. I have a few off-cuts of plasterboard so I cut one to size and made two holes ready for the downlights. I had to add three additional timber supports into the void to support the edges of the plasterboard, at the sides and in the centre. I then wired the existing supply cable into a junction box screwed into the ceiling and wired the two supplies to the lights here. All pretty straight forward and once the panel was screwed into position with the light inserted I turned the power back on and all worked well.
I have also the option of adding up to three additional downlights at the back of the room but having turned these two 35w halogens on I'm not sure I'm goint to need them - these appear to provide ample light and in fact I might well replace the basic light switch with a dimmer.
I have to decide on how to finish off the plasterboard and conceal the screws but for now it at least looks a lot better than my ad-hoc bulkhead.
Photo after (to follow):