Tim Bray, co-inventor of XML and current Google Developer Advocate, has submitted a draft proposal for a new HTTP status code that will be shown when access to a web page or online resource that has been requested is blocked due to legal reasons.
The new 451 Unavailable for Legal Reasons message would appear if users are denied access due to state censorship or some other legal block, such as the recent UK ISP-level blocking of The Pirate Bay. When used correctly the code should also show information regarding the relevant legal restriction, the legal authority behind it and what class of resources the restriction applies to.
Being a draft, the idea is still some way from being a standard but could be adopted if approved by the Internet Engineering Task Force (IETF).
With regard the current UK restrictions, some ISPs are using the 403 Forbidden status code but it has been pointed out that this is wrong. The 403 code is supposed to be used when the server has received the request but refused it. However, in the case of a legal block the server will never have received the request.
Whether we will see this code adopted is perhaps unlikely, as Bray points out in his draft. With the proposed code being optional, "it is imaginable that certain legal authorities may wish to avoid transparency, and not only forbid access to certain resources, but also disclosure that the restriction exists."