I've just uploaded "Guarding your IPR" onto my personal website. This mentions the British Library's "Currentscan" service and some info on private investigators who can be relied upon including, in particular, Rosy Amsel who works in Manchester not far from our old chambers address. Rosy is a very entertaining companion as well as a good PI.
If anyone knows of any others I should be glad to include them. I should be particularly pleased to list any private investigators based outside the UK who are recommended by an established IP lawyer, patent or trade mark agent.