My local home brew shop reckons the additives to clear a brew are made specifically for beers, and adding these to ciders is a no-go as it'd change the flavour too much. They mentioned if I wanted a clear cider, I'd have to make my own brew and add in Irish moss.
Buying juice in the supermarket and adding sugar and yeast won't allow this, so the best I can do is let it sit, syphon some off the top into another bottle and let that sit until it settles. It'll never be perfect but it's not too bad.
I'm keen to do my own from scratch which will hopefully produce a better brew.
Thanks everyone for your help.