Request identification & solving of the white mildew on my Beech Tree, please

There is a condition called Beech bark scale, and if it's that, it's widespread. Usually a white powdery substance appears in crevices in the bark, especially on larger branches and the trunk (which is what we see here, only loads of it). It's caused by a sap feeding scale insect (felted beech coccus). Has little direct effect on the tree, but it MAY make it more susceptible to beech bark disease (a canker). Control by spraying reachable parts of the tree with a tar oil wash in mid to late winter. The scale insect causing the problem should be underneath the white deposits - they're small and orange - so if you can find them underneath, that's what it is.