For 2 standalone maisonettes with an entry/exit via a single external metal staircase would a Fire Risk Assessment required?

and if so, practically speaking,  given the staircase itself is non-flammable what would an "assessment" entail?

We would need more details of the layout and what you mean by 2 standalone maisonettes.

Are these above ground floor commercial units with access via a rear external stair?

Thanks for your reply, yes thats correct, there's one commercial shop below and two flats above, with no communal areas. The flats are accessed by a single external metal staircase.

What would be required in this instance?

Thanks,

Andy

If the single external metal staircase is used by both flats then that is a communal area therefore subject to the RR(FS)O but the FRA would have little to considerer other than the maintenance of the external, however the commercial premises below would have to consider the flats above when conducting their FRA. 

As above. The FRAs would have to consider the effect of a fire in the shop on the ceiling separating it from the flats as well as it's effect on the ability to use the stair.