How can I vote in EU parliament election (from the UK)?

I live in the UK but I am a member of another EU nation (Sweden). I want to vote in this years EU parliament election next week. However I have never previously voted and I have not yet registered on the electoral roll (that the council runs). I find the system with electoral registration confusing and I don't know what I need to do! Please, please help me with some clear instructions on what I need to do!