Changes to the rules on using cookies and similar technologies for storing information
ico.org.uk/~/media/documents/library/Privacy_and_electronic/Practical_application/cookies_guidance_v3.ashx
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
The law which applies to how you use cookies and similar technologies for storing information on a users equipment such as their computer or mobile device changed on 26 May 2011. This document sets out these changes and explains what steps you need to take to ensure you comply.