Thanks for that. I didn't burn in the sky at all, there was adequate tone in the area which equated to the density that I remembered but simply the wrong colour.
No I have never needed a reduction mask but I would be interested how to. I don't think that it would have made any difference in this case as there was very little in the way of contrast variations. The shadows that were there did come out bluish as I would have expected but not the sky - very odd. The image is not really an important one so will leave it until I have more time to experiment. Thanks anyway.