Have a look at this page of the Gardeners World site -http://www.gardenersworld.com/how-to/problem-solving/garden-pests-nail-gall/

Yes, it is nail gall. Believe it or not, they don't really harm the tree that much. Many tree species ans other plants have their own particular species though not all gall mites are of course as harmless as occasional Blackcurrant growers or yew tree hedges attest to!

yep, Lime Nail Gall - and Fractal, hooray, its been so long I actually checked the membership list only yesterday to see if you'd left...

:)

Thanks for that, our local park gardener, (and so-called expert!) said he though it was caused by the recent dry spell, I'll be able to enlighten him now, cheers people.