Horrified Press is a UK small press specialising in horror. It has several imprints and is currently closed to novel submissions but always needs stories for anthologies. There is a long list of them at the open submissions page, some with open deadlines, others with fixed dates.
Forthcoming open anthologies are Jack O’Lanterns, for Halloween horror stories, and Welcome to the Dance, for stories about dancing (eg dance with the devil, dance with death, although wider interpretations of the theme are encouraged by Horrified Press).