[nknight]

> The law is the law as it's written and then as it's reflected in court decisions.

That may not be as true as you think.

I don't really know how the modern UK legal system works in this regard, but in the US, the courts would A) defer to the interpretation of the agency (in this case the ICO) as to what a statute means, and B) greatly frown on any attempt to prosecute without warning people who reasonably relied on the agency's declarations.