That is a very narrow space and steep stairs, you could go for white washed tongue and groove panelling up the stairs at shoulder height with a moulded top to finish it, then use a light oversize patterned paper on the walls, or maybe use William morris wallpaper on the risers like this?

Have you investigated the state of the stairs under the carpet? If they are decent, exposing the wood stair might be a possibility. If so, a warm or dark finish against a crisp wall. If you prefer to not have the noise of foot traffic, a runner with only a small margin could work. You might be able to work in a natural finish rail , or rope and wood combination rail as am thinking any rail would have to be flush to the wall so as not to encroach on the passage.

The expanse of wall - hmmm. I think i would leave the walls at the side ornament free, and just paint. But the window wall could make a great gallery wall... pictures, mirrors (antique styles or interesting frames), narrow shelves for ornament/ books, or those ikea picture shelves so frames can be rearranged or updated. You might even consider a hanging - a tapestry or a drop of material that you find attractive. The hanging might even inspire your color choices. It may work to use only the upper section, leaving the lower section clear to walk through or the space may even allow for a combination of these suggestions. Enjoy exploring the possibilities!

On looking at your pics again, am thinking mirror gallery or a hanging - it could stay as a static display (coz I would want to be getting up there again in a hurry!) Mirrors would help to bounce light around as any light fitting would need to allow good illumination as well as interest.

@kingfisher: thanks for your message. I wanted to incorporate some William Morris wallpaper in the house and I haven’t even considered the steps. It would certainly make it quirky!

@kazzh: it seems you put some thought into it and I really appreciate that. I haven’t checked what’s under the carpet yet but I like the idea of keeping it simple with a paint and maybe create a gallery by the window wall. Sounds like a cheaper option to keep costs down.

@Sonia: love the idea of panelling it white I think this would be an investment for a later stage.

I would be looking at St.Judes fabrics and wallpapers as a source of inspiration for old cottages.

Also take a look at Kettles Yard House in Cambridge, it's a lovely place to visit when lockdown ends.

https://www.stjudesfabrics.co.uk/products/compton-verney-mark-hearld-river-blue

I live in an old cottage too, with a narrow staircase that joins onto the living room. Like yours, the original carpet was green, which I am having replaced with a dark grey wool carpet, just make sure that whatever you decide to do with the stairs works with the room at the bottom of the stairs. The white walls looked cold so have been repainted in F&B skimming stone and am just adding a vintage glass pendants at the top of the stairs - see link below. Will probably add some artwork to the narrow walls. I have kept it simple as I’m not keen on William Morris or anything too fussy. It can be a challenge renovating an old cottage so it is in keeping with its traditional style without looking dated!

https://www.google.co.uk/search?q=david+hunt+aspen+light&ie=UTF-8&oe=UTF-8&hl=en-gb&client=safari

BTW William Morris have some lovely wall tapestries - not my kind of thing but if that’s your style it would look good in a cottage.

@Andre - glad you enjoyed my musings. Your pics inspired my inner designer!

@colourhappy: thanks for sharing the fabrics from St. Judes and also for the heads up about Kettles Yard. It looks like a great day out!

@macbroom: I was considering a hessian carpet in the room at the bottom of the stairs and will probably consider using it on the staircase if the wood underneath is not great. Ps: love love love the light you sent but I think I’ll try to be more adventurous with a more cottagy and less modern kind of look.