Thank you both for your help, - I apperciate it.
I managed to figure out in the end that it basically boiled down to what Greggles said, in that the 3rd generation ipod was geared up for Firewire as oppose to USB. Hence most of the 3rd party USB chargers wouldn't work. The annoying part was how little information was on the packaging about this though, ie which models the chargers were designed for.
Yesterday I managed to get sorted anyway; Found a compatible 'mains charger' and also a combined 'USB/Firewire - Dock Connector Cable'. ie I can now charge and sync the iPod.

Got them both at Maplin which I guess is maybe the first place I should have thought of for obscure cables!
The final thing I'm looking to buy is an iTrip and car charger. Given all the issues I've had in sourcing chargers so far, I'd have preferred the original model of Griffin iTrip - ie the old cylinder shaped one which plugs in the top headphone socket and leaves the bottom dock connector free for charging.
Looks like I might struggle to find one of these now though unless anyone knows any different?

They are available on a few oscure websites but I was hoping to get one for Christmas and therefore would have preferred a high street store...