What is on this apple tree?

Can anyone help please?  I work in a garden where there is a large old and tall crab apple tree that has lots of white wolly bits all over it.  I think this is woolly aphid and wonder how I can get rid of it organically or will I have to use chemicals?  I am in a hosepipe ban area so cannot hose it off.  Are there any nematodes that will clear it?  See picture below. 

Many thanks for your help.

It does look like woolly aphid. There are no organic controls other than scrubbing them off with a stiff brush, I'm afraid.

There is a list of sprays available here.

Very similar sort of thing is Oyster scale. Just as hard to get rid of too. The white is a waxy substance which protects the insect from the outside. Water based sprays cannot get through it so insecticides do not work. If only a small amount then as suggested scrub it off, add some Horticultural soap to the water, it dissolves the wax. Or use some Methylated spirits. That also dissovles the wax and the insect dies.