Know what's wrong with my Apple tree?

This grey/white mould(?) appeared during the very wet winter, I'm not sure what it is. Was very concerned it was Honey Fungus but it doesn't go beneath the surface of the bark and (from what I understand) Honey fungus works under the bark. The bark does seem squashier than the bark that is free of it. It doesn't seem to be affecting the moss or ivy that is growing up the tree. Any ideas? I'm a bit worried about it 






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http://www.britishlichens.co.uk/pi_crust_sterile.html
and this.