As many; Framers, Drywaller's, Tapers and Painters know 2 & 3 rung step stools have been a point of contention by MOL inspectors for many years.
In 2015, the ladder regulations were revamped and in November a new definition of a 'step stool' has appeared for the first time.
“step stool” means a self supporting, portable, fixed or foldable ladder, not adjustable in length, and having,
(a) a height of 800 millimetres or less, excluding side rails, if any, above the top cap,
(b) flat steps, but no pail shelf, and
(c) a ladder top cap that can be stood or stepped on;
In my opinion this new definition should clear up any confusion about use of 2 & 3 step stools that are under 800mm and where the manufacturer allows standing on the top.
Remember section 93(3) if you are following the manufacturer's instructions on any piece of equipment, there is no reason you should have to worry about MOL charges. Should charges happen anyway, you may have a valid defence, provided you were working in adherence with the manufacturer's instructions.
As seen in Werner Ladder manufactures picture, they do allow to stand on the top of their 'work stand'. Also they list the maximum step height on the 2 step as 1'11".