I think they should take on the guy in the UK courts as this is akin to filing for a case in a foreign jurisdiction when its clear the other party may have no way to defend the case, thus weakening the importance of any judgement.
Simple libel or even human rights act laws cover this case in the UK so theres no reason to file it outside of the UK except to create possible hurdles to representation and worse it could indicate the case may be weaker than claimed and thus they have cherry picked the court to file complaint in to gain an advantage.
I think both sides in this are playing a poor game of morals disguised under the veneer of a DMCA case, the classic "I don't agree with your views" argument turned nasty, in such cases there is no winner.