Following on from my question, a few days ago, about how people have been treated if they fall asleep at work, I went to Occupational Health today and so can report on the outcome.
The OH doctor was very supportive. Providing I was not a danger to myself or others I could continue working as I am. I have been working with tiredness for years and there have been no problems yet. The situation needs to be assessed but it can be something simple like ensuring my work area is uncluttered or has no dangerous chemicals immediately in front of me (seriously folks). That way, if I fall asleep and fall forward, I don't injure myself (!). Working with a machine featuring a very sharp knife is a tad problematic (!!) but I could ask to do other work if I get sleepy using that. Otherwise, it should be common sense solutions like taking breaks when needed for stimulants or fresh air.
The OH doctor's logic was that if I regularly only get between zero to 3.5 hours sleep a night due to RLS, then I'm going to be tired. We'll just have to see how my boss reacts now, it may be a simple: "we can't have someone falling asleep at work" and start some sort of action against me. The legal protection mentioned before means I can't be discriminated against; they just have to do a work assessment so I can work on with my "disability". I remain suspicious but will keep you posted. If I'm lucky now, the missus has gone to sleep up stairs so won't be disturbed by any residual kicking or the noisy hum of the CPAP machine when I go up, then I can try to get some shut-eye...oh the joys!