Share 'Sherlock Holmes'

Hi. I've noticed quite a few series lately featuring Sherlock Holmes in some form: comic book Holmes, Enola Holmes (younger sister of Sherlock) and other young adult novels, and other adult mystery spin-offs. Has Sherlock Holmes gone into public domain? I imagine that the UK rules are different than for the US. And where does a person go to find out if a novel has gone into public domain? Thank…