Slight change of plan. I found that Maplin do in fact sell sealed pushbutton switches, and they look exactly what I need. I require two of these; one for the horn push and the other for the brake test switch. I have a battery discharge monitor circuit to wire in (as the bike cluster has no equivalent alternator light). I already have a small microswitch for programming the rev light (as it will not be used that often - the switch not the rev light!). Also on the way from Maplin is lots of little grommets, small heatshrink and small metric nuts / bolts so that the job will be done properly.
I have also ordered a 52mm LED cluster that I will use as a fog light. It only cost £10 and looks a little more out of the ordinary than the other types of fog lamp available. I have decided to retain the existing fog light switch because it satisfies all of my requirements apart form it not being waterproof. To this end I'll install it under the dash on the central tunnel panel so that it can be seen but is unlikely to get directly wet. It may need a small bracket to fasten it correctly.
Whilst waiting for that lot to arrive I can continue on with the other tasks, still remembering that I have yet to obtain a clutch cable and a throttle return spring. Whilst it remains sunny I can start by torquing up the rear of the car, applying my lovely pink nail varnish as I go. This will enable me to see where I have already done and also (if it comes off) indicates that the bolt/nut has possibly moved, especially important when we're talking about propshaft bolts.