In the latest info on Friday.

http://www.ico.gov.uk/news/blog/2012/updated-ico-advice-guid...

"Implied consent is a valid form of consent and can be used in the context of compliance with the revised rules on cookies."

Here are some selective quotes from the document, I take it to mean: tell the user with a clear message at least once (ideally get them to click confirm but it's not a requirement):

"In some circumstances those seeking consent might consider implied consent as an option that was perhaps more practical than the explicit opt-in model... For implied consent to work there must be some action taken by the consenting individual from which their consent can be inferred... This might for example be visiting a website, moving from one page to another or clicking on a particular button... The key point, however, is that when taking this action the individual has to have a reasonable understanding that by doing so they are agreeing to cookies being set."

http://www.ico.gov.uk/for_organisations/privacy_and_electron...