‘you need to be qualified to use a ladder at work’
This is not true, you do however need to be competent. This means having the necessary skills and knowledge which can be obtained from working at height training courses.
‘working at height includes walking up and down stairs’
working at height does not include walking up and down stairs in a building.
‘HSE has banned the use of ladders to access scaffolds and you will be fined if you ignore this ban’
This is not true, Ladders can be used for access as long as they are of the right type, in good condition and effectively secured (tied) to prevent movement. You should ensure they extend at least one metre above the landing point to allow for a secure handhold when stepping off.