On Monday, 14 September 2020 16:15:08 UTC+1, Jac wrote:
I have a flat roof ( old conservatory ) attached to two sides of my
house, do I need planning permission to add an external staircase
& some railings to make it an additional outside area ?

Planning permission *and* Building Regulations.

Planning will involve neighbour notification and overlooking is likely to be a significant ground for objection (unless you have a big garden or are somewhere rural).

And a "former conservatory" roof is most unlikely to meet the strength requirements for a walkable-on area.

Owain