I want to paint my floorboards grey , What type of paint do i use and do i need a protective varnish on top?

I live in britainI want to paint my floorboards grey , What type of paint do i use and do i need a protective varnish on top?
porch paint will hold up well and gray is its most common color.when i was in the army we added 20% polyurethane and mixed it in.it gave the floor a nice shine.I want to paint my floorboards grey , What type of paint do i use and do i need a protective varnish on top?
Sand down. Apply primer ,undercoat and gloss. For a very durable finish apply a coat of Ronseal Diamond hard varnish