This new paper by Hall et al (May 2013) finds that an unexpectedly low percentage of firms patent in the UK, and it offers explanations of why that is the case.
From the conclusions:
Our descriptive analysis shows about one third of UK firms report any form of innovation. Strikingly, we find that only 3% of firms in our sample patent and that even among firms that conduct R&D, only 4% patent. In particular, the share of patenting firms is much lower than what one might expect given that around 20% of firms that invest in R&D report product innovations.
The paper is titled "The Importance (or not) of Patents to UK Firms."