Confidence: It's likely to be this, but I can't be certain.
Notes: This doesn't look like either R. emetica OR R. nobilis to me, and there doesn't appear to me to be any beech in the litter either. However the evident habitat, acid oak woodland (note the Luzula sylvatica in the background, and visible leaves are Sessile Oak, Quercus petraea) is right for R. silvestris (= R. emeticella of the Rayner keys). The precise colour of the cap and habit are exactly right for this species. I am not posting with the highest level of confidence as Russula is a too critical genus (but I'm sure really). It is a common species in sites I know well. Alan