I thought I should post an update. Last month my mum decided that she didn't like my modelling supplies (paints, glues, etc) being piled up in a corner out of the way in my room, so she put them all away in my new chest-of-drawers and inadvertently ended up squashing everything I'd done on the helmet so far (as I had stored it in there to try and keep it from being accidentally squashed, ironically). I've had a look at it and the front of it is OK, although it needs quite a lot of work to re-attach a few things, but the back is completely squashed and bent out of shape so its probably going to be easier to start again on that bit.
I have thought about leaving what I've got where it is and just restarting from new again on this. I've been looking into more cardboard and am looking at some slightly thinner stuff (which should be easier to bend and, hopefully, not tear apart so easily at the joints) and comes in a pack of 250 sheets, more then enough to do a complete set of armour should I decide to (the other pack I got was only 24 sheets). It'd also be a good chance for me to get new glue (the one I got before wasn't as strong as I'd hoped) and a new pair of scissors (as my current ones are broken).