Stunted ash shoots, ideas?

[sloth]

Firstly apologies for the poor pics taken on my phone. I noticed this roadside ash near to where I live is showing odd symptoms, hopefully you can make out some detail in the pics...

I didn't think to get a context shot, but overall the tree looks ok. Scattered throughout the crown some shoots and leaves are stunted, thin and distorted, while the rest are fine. The tree is about 20 feet tall, and well surrounded with concrete.

My intitial thought was aphid or some other sap sucker, but can see no evidence of this. Nutrient deficiency maybe, but wouldn't that affect the whole crown?

Any thoughts welcome as I'm a little curious, cheers

[Graham]

Possibly 'sports'. Viral origin?