Silk button spangle galls and I think some common spangle galls. Created by two subspecies of wasp - you can get more info from @jantan's picture which I thought I was sort or 'nicking' but it turns out that most of these galls are quite different. http://365project.org/jantan/365/2013-09-14
I have never seen these before , they must only hang out in Cambridgeshire & the southern half of Britain. I wonder what happens to them next ...do the y hatch or stay until next Spring...must check up! great title!!
Now I've seen yours and Jan's :o) xx