Not denying the holocaust per se, but we do have vilification laws of which is what his court case was about. He was charged with vilifying Jewish people.

The arrest in Britain pertains to 'hate crimes' and 'defamation of the dead' laws from Germany.

This is a sticky one. I'm not sure I really have an opinion of posting on the Internet and the jurisdiction of laws. It does open up a whole can of worms legally though.