I found many examples of the following gall on catkins of an evergreen oak in the main campus of Nottingham University. I have not identified the oak with certainty, but suspect that it must be a Lucombe Oak Q. x hispanica (cerris x suber) or similar hybrid. It's leaves were extensively mined by Phylloronycter messaniella.

Leaves, catkins and galls: http://www.flickr.com/photos/mausboam/3548167069/
Catkins and galls:  http://www.flickr.com/photos/mausboam/3548977560
Galls:  http://www.flickr.com/photos/mausboam/3548976306/ 

I would therefore assume they are sexual galls of Andricus grossulariae. Oddly I'd looked for this on Turkey Oaks earlier in the day. Obviously I'll seek confirmation of the identity of the host; I'll probably go and have a look at one or two other Lucombe Oaks locally.

Regards,

Jerry Clough