Assuming the staircase is steel, clean, dry and prepared as detailed in the techncial data sheet we can recommend Rust-Oleum 769/780 Damp-Proof Rust Primer followed by Rust-Oleum 7200 Floorcoat PU on traffic'd areas and Rust-Oleum 7500 Alkythane on the other areas. These are available in many RAL and BS colour options in a satin or gloss finish.