This sounds ;ole a bird I saw the other day in Snowdonia . Dull day so not sure if grey or black but the wing bands were distinctive. It swooped in front of our van and flew down lower into the valley so we could only se it from above. Can't find any reference or picture of bird with such wing bands. Most pictures show birds from below [logical]. It had long wings and fast wing beat. Nearest I've seen in illustrations is a shearwater but they don't seem to have the wingbands and what would a shearwater be doing in the hills about 20 miles inland?
We do have red kites here but whenever I've sen one, it has glided not flapped its wings fast.and they do fly below me where I live and have never seen white bands on top of wing.
Daffni