Hi Alistair I think this image straight from camera is excellent and shows you have the camera skills to balance light and dark correctly to get the image you want. I look at images such as these as abstracts more than anything as they tend to feature shapes and tones more than anything else.
If this was my image I would look at doing 2 or 3 things to help in my view improve the image.
1. With a perspective view such as this I would bring the focal point as near as possible to the centre of the image, this allows the railings to frame the view into the focal point. If possible keep the free space equal on both sides of the image.
2. You have 1 rail higher than the other so I used a skew function in GIMP to level them off and keep the geometry of your image.
3. Finally after all my adjustments the uprights bowed slightly so I adjusted the perspective on both sides to make them vertical again.
I have not adjusted your colour or balance as I think the soft colours work very well with this image.
Let me know what you think of my adjustments.