It's lichen. It's harmless, it's a sign of clean air. My trees are covered in it in all shapes, sizes and colours.
Zooming in I think it is woolly aphid. Not good.
Fungus produce spores...they are microscopic...more like dust.
Do report back here what you find on closer inspection.
I had another look this morning and it certainly looks like it could be this wooly aphid you speak of. I showered a but of water on them yesterday and it seems that its washed away some of the 'wool' and I can see an outline that reminds of a woodlouse. They don't look like they're moving however. Please see some close ups. I've also attached a photo so you can see that they are clustering all over the tree. It really doesn't look good.
I think I'll have to get the landscaper back and see what he makes of it.
Many thanks you did very well to diagnose the issue using the first photo😊