soot like stuff on leaves on my bay tree

These are Aphids deposits.

You have a sort of scalely bug, give it a good wash with very weakly diluted washing up liquid , it should help.

I go with scale insects, you can see them on the back of the leaves, usually along the mid rib, like little limpets. they do secrete a honeydew like aphids which is then colonised by a black fungus, sooty mould. I get this problem frequently on my bay too. You can also buy an organic treatment based on fatty acids if you have a large bush