What it needs however is something just to give it an edge.
I bought one of those "5 Voices in One" fancy dress voice disguisers and it was total cr@p - BUT if the sensitivity of the mic had been half decent (you have to be pretty loud or it keeps cutting out), and the resulting voice hadn't been SO, distorted it would have probably done the job for us (especially in the cardboard helmets - http://www.bazookajo.me.uk)

Anyone come across a decent one on their travels that might fit the bill?
Many thanks in advance
Joe.