Neville care to share how you edited the image?
First of all, Peter, I should say there was a lot of trial and error in this. I opened the file in Photoshop CS6 and started by using the lasso tool to select the parts of the left margin that needed adjustment. I feathered the selection to, as near as possible, equate to the gradient of light to dark which I wanted to correct. I then used 'Curves' to adjust the luminosity of the darker area to almost match the area to the right of this selection. I then inverted the selection and using Curves again I lowered the luminosity of the rest of the image. This did not entirely to the job for me. The top and bottom left and top right corners still needed some levels adjustment and these were selected and adjusted separately. As is often the case the adjustments pretty much corrected the luminosity but the selections needed further colour balance tweaking to get them right. Also the much adjusted top left corner now showed significant noise type artefacts so, given that it was sky with no detail, I applied Gausian Blur Filter to the feathered selection. I then made some minor adjustments to the sun and parts of the right side of the image (using feathered selection) to restore the luminosity and colour as close as possible to the original. Finished off by dodging and burning around the image to iron out any obvious inconsistencies.
Hope this helps.
Very much so Phillip thank you for taking the time to explain how you went about the editing. I shall with your description in front of me revisit the raw file and see if I can produce an image which retains all of the frame including the problem sun but without the dark banding that I originally introduced.
Thanks again for explaining your approach, I shall use it as part of my photoshop learning curve
You are most welcome Peter. It should be much simpler working from the original raw file. I think I would just select the highlights containing the sun and its bright reflection on the water but excluding the blue area above the sun. Probably the lasso tool is best but the real challenge is the degree of feathering. Trial and error. Use curves to make the adjustment. Looking forward to seeing your second version.