Getting Started
Wherever you are, there's probably a writing group, a writers' support network, or writing classes to help you get started -- and keep you focused. Local libraries often act as a hub for writerly activities as well as providing the most important inspiration: free books! There are also increasing numbers of writing groups online -- Facebook is full of them -- as well as online writing tools/sites like Juliana Spahr's awesome cybergraphia.
But face-to-face workshops and reading sessions still have a lot to offer. Here are some UK- and London-based organisations:
Getting Published
There are hundreds of magazines, both online and offline, that are open to zinging new work. Take a look through their online archives, or pick up a copy in a bookstore or library, subscribe if you can, before you submit, to get a taste for their cup of tea. 
Some current UK magazines with open minds and excellent ears are:

Small publishers often accept unsolicited manuscripts, but have stringent submission guidelines. Get familiar with the guidelines, and with their publications. Nothing makes a small publisher happier than someone buying their books.

UK poetry publishers worth reading and contacting include: