Send a U2U to jamcoly as he's just got a new chain, front and 2 rear sprockets for a damn fine price off of ee-by-gum-bay
If you hadn't said you have a lot of slack in your chain I'd say you were having difficulty getting neutral cos it was too tight (eh Pete!!!), as it is you're probably not getting full plate release in your clutch (clutch drag) and either need to bleed your system through (how close to the handlebar does the lever come when disengaging the clutch?), maybe you'll get away with just trying to adjust your clutch lever span out a bit so you get more movement