Nearlythere,
I think your query is more a question of semantics than of practical fire safety. You can infer from the CLG quote that there do exist spiral staircases designed for means of escape, and that might appear to be the most obvious implication.
But the loose wording of the CLG statement means that it can also simply mean that there are existing spiral staircases and that none of these have been designed for means of escape and so they should not normally be used for such a purpose.
In fact, I believe the former interpretation is the right one. I have seen a number of spiral staircases that were designed for means of escape. Most of them are at least a hundred years old and would be judged perilous by today's standards but, it cannot be denied, that they were installed to provide an alternative escape route.
Coming to the pertinent fire safety aspect of your query, you have to ask yourself, can these four people safely and reliably use the spiral staircase to escape from fire? I would suggest that if they are in the habit of using the staircase on an everyday basis to access the sleeping area then they would be perfectly capable of using it to escape from a fire. If they have never used the spiral staircase and some part of their disability makes it difficult or hazardous for them to use the spiral staircase then it is not a viable alternative.
It is slightly more complex than I have stated above because you have to consider, not just the residents, but also other people that might be in the bedrooms and also other residents who may occupy the rooms in years to come.
Many existing spiral staircases provide an alternative (or sometimes the only) escape route for a small number of people. Have a good look at the staircase and a good look at all the people who might have to use it, then make your judgement.
Stu