As a general rule, ladders should be placed on level ground to maximise stability while in use. The Health & Safety Executive (HSE) guidelines say:
"You should only use ladders in situations where they can be used safely, e.g. where the ladder will be level and stable"
This rule would appear to preclude the use of ladders on stairs. However, if you do need to get a bit of extra height while working on a staircase, we may still be able to help you.
If you've got a lot of different jobs to do - but you don't want to buy a lot of different ladders - then a combination ladder may be the ideal solution.
A combination ladder is a multi-use product that can be configured into a number of different shapes. For example, a 3-in-1 combination ladder might serve as a step ladder, an extension ladder, or a stairwell ladder depending on how you set it up.