Katex - wash your mouth out - Hyndburn has more open space per head, than any other area in Lancashire. Tons of places to hold events - Broadway, 8 parks, Sports Centre car park, playing fields like Whiteash in Ossy or Memorial Park in Gt Harwood or even the green space near St James' Church.
Anyway, apart from that, I'm not really sure what you're trying to do. Is it a music concert or a fete, is it a charity event or free event, could it be tied in with the carnival or any other event or does it have to be a stand alone event?
Good luck, if you need any help or advise feel free to pm me as I do this sort of stuff all the time around Hyndburn.