Hi Ben,
Two things: first, apart from the small twigs, you haven't had enough 'brown' material - things like shredded bark, straw, paper - my mind's gone blank but someone will shout up, I'm sure. Secondly, with so much 'green' stuff and not enough brown you would expect it to turn into a slimy, stinky mess. You've avoided this by keeping it so dry. Unfortunately, it's not going to rot down if it's that dry.
My suggestion would be to tip it all out and restack it. If it's standing on earth, rather than concrete, turn over the soil a bit to encourage the worms to come up, and stand the bin on top of that. After that start refilling, but this time do a layer of your green stuff (by the way, I'm pretty sure chicken poo is 'green stuff'), then a layer of brown. Green, brown, green, brown.....
And give it a good soaking. Dig up some worms, or buy some and chuck them on the top. Any slugs or woodlice you find can be put to work in there as well. It wouldn't hurt to put the odd layer of garden soil in there as it will be full of the right microbes and creepy crawlies, but don't worry if you don't have room.
If you're really struggling to get it all in, store some of it in a sack for a couple of weeks until the level has dropped a bit. Also, if you can't fit in any more of your lovely chicken poo, try making it into a fertilizer
I asked how to on this thread but unfortunately I keep knocking it over and having to start again
