Anna
I think the reason no one has replied to your query is that the use of steps is not considered as much of an issue. They are as you say, a neccesity, but not governed, as far as I know by any regulations such as ones that apply to extension ladders. The usual Health & Safety practices and a bit of common sense should be ok, oh and a suitable Public Liability Insurance Policy!
Hope this is of help, Jake (Westclean)