I think without spending too much I would recarpet the stairs with a strip of carpet in the middle, maybe use the brass carpet clip things you can get from antique and salvage places. Apart from that I would only say a lower less intrusive radiator might look nicer, its a bit much at eye level you could also introduce a mirror on the left hand wall, this might bounce a little more light around.

In my opinion the green walls clash a bit with the carpet. The carpet goes with the floor regardless of whether it's dirty or not. The walls look cool grey green and the carpet which is similar in value looks taupe (contains red or red purple). This is why it looks a little off. Something like a warm neutral such as a warm stone colour might make it look more cohesive. If you want to keep the wall colour it looks good with rich woods and something like a sisal or natural floor covering.

I would suggest to recarpet the areas, paint the walls light colours (cream) and add a contrast colour on the smaller walls (yellow/mustard). Get a nice long console table. I got mine from Harvey Norman. Complement that with mirrors on the wall, pictures or wall art.

Love the Crittall idea - we had a few similar projects and turned out great. We would add a Crittall door going into the room.

For a little bit more drama I would consider repainting below the dado in a stronger colour, this will create more interest, be better at disguising scrapes and marks that you inevitably get on stairs.