Floors don't need to be darker than the walls, but a darker floor visually grounds the space and if you have a light colored floors with dark furniture it would make the furniture appears to be floating in space and it's just not a pleasant room to be in.

You could use lighter floors with an area rug that pulls all the colors in the room together.

Hi bythsea, Marie here. OK - you don't have to do anything in design - it is all very interpretive and important to get the feeling and vibe that you want to portray in your home. However, naturally, our genes are used to seeing darker colours underfoot (earth) and lighter colours above (sky), anything other than that can be unsettling and a bit unnerving. We have all done it though, and would be interesting to see if people living in these homes with light floors dark ceilings feel unbalanced? Below are photos of light floors for your inspiration, I'll send photos of dark floors, light ceilings in next...

HI again bythsea, Marie here again, here are photos of dark flooring - notice that most of these rooms either have very large windows (south exposure) or are large rooms to handle the dark floors...whereas light floors are great in small spaces - and with white or light walls, make bright, airy spaces...

Thanks all of you! ...and especially for the picture Marie - I've found it very hard to find pictures of rooms with darker walls & ceilings than floors.
I've decided, I think, to go with a blonding / transparent white wash for the walls to let the room ease off a little (it's currently all wood) and will let the ceiling and floor keep their oiled colours (they'll get darker with time I think?). The ceiling is going to be a tone or so darker than the floor but I'll see how it goes..
Our furniture is all ash and elm so it shouldn't float too badly.

I appreciate all the comments - and the pictures!!