This picture, taken a day later, shows that Theory 1 in my last blog post was correct. There are no luminous lit up clouds in the far distance. They are all grey. The distant patch of sea is clearly being lit up by sunlight shining back through holes in the distant cloud. So it can only be that the vertical wave surfaces are reflecting the sunlight back in my direction. I had binoculars with me on this occasion and was able to confirm that it was true.
