We can't list every poetry competition here, but the good news is, there's no need to - these sites do it for us:
Poetrykit.com - thorough listing of current UK (and many other English-language) Poetry Competitions with links to each competition's site.
Prizemagic.com - Idiosyncratically-written but comprehensive listing of current UK (and many other English-language) Poetry Competitions, ongoing, then in deadline order with links to each competition's site.
Duotrope.com - an award-winning, free writers' resource listing over 3400 current Fiction and Poetry publications, with a free Submissions Tracker for your own work. Highly recommended.
WriteOutLoud.net - useful resource for (especially performance) poets in the UK. Create a poet's profile of yourself and your work, list your events, catch up on poetry news and competitions, join discussion forums.
National Association of Writers in Education - supports the development of creative writing of all genres and in educational and community settings throughout the UK. Professional directory, handy eBulletin with opportunities, courses, events.
BBC's On This Day - day by day listings of main world news headlines on this day in recent years