Oak Galls (?)

Along the fence line in one of the paddocks behind our friends' house are a variety of trees including an oak ... which has many normal looking acorns but around half of them have these growths springing from the acorns and occasionally enveloping them.  Apart from a couple of ants I didn't see any insects or larvae but a little googling suggests they are caused by Gall Wasps.  I'll add in a couple of extras,  one of the leaves and another of the galls,  in case anyone has some more specific ideas.

Macro lens shot,  with flash and I used a monopod to keep things relatively steady.

Edit - likely a knopper gall,  and the wasp is:  Andricus quercuscalicis