I'd be grateful for any pointers to the relevant regs covering external
steps from back doors (one conventional, one patio) into a garden. I've
looked online but for some reason can't find exactly the information I'm
after.

The drop involved is 24" / 600mm and the steps will be going onto a garden
surface which currently is grassed but will eventually be paved, so there's
a possibility that whatever steps are built now will eventually have to be
replaced if they can't be removed, adapted and refitted.

There will be two separate sets of steps, the widest around 39" / 1m. These
steps are from a recently-built rear extension and the work can't be signed
off until they're done, so I need to know if (for example) side handrails
and bannister-type railings are necessary, and also any standards regarding
materials and strength.

Many thanks.