Get at it with a lump hammer, Sue.. What's the worst that can happen EH? I don't think anyone will give you an 'absolute guarantee' without seeing it in person - to rule out anything weird or wacky - but at KK says, it's usually a stringer, not cupboards underneath. Take a couple of panels out, expose the bottom of the staircase to have a look with a torch and you'll most likely see exactly that. Then have at it with a lump hammer.