Wouldn't this be easier if browser companies blocked all cookies by default. Users wanting cookies turn of blocker? A lot less browsers than websites?
The ICO has the power to force browser vendors with a UK presence to implement this at the browser level. I wonder why they didn't? Short-sightedness? Or perhaps they knew that Google/Mozilla/Microsoft are more capable of presenting a unified front to fight this, compared to however many thousands of web developers are affected.