The FSAI did a public consultation last year on words you can use on food products (including drink). Their new guidance note for producers is now published here[/url:2le0kn1l] [PDF].
Artisan, Farmhouse, Natural and Traditional are the terms it deals with. I can't think of any of the breweries that use the term "artisan" in their marketing, but now they're only supposed to if they make an average of less than 1,000L per week. That can't be many breweries, can it? They also have to employ fewer than 10 people.
I guess that in the same way that we now use "craft" to mean microbrewed we could also use "artisan" to mean nanobrewed.