Its sitting as far down the battery terminal as its possible, the negative terminal is smaller than the terminal for the positive.
I'm really pissed of by it all as I'm sure they will try and get out of taking responsibility and its the unknown of what else could have been damaged that may materialise over time. Maybe the radio has its own fuse once its out and that may resolve that. I will get them to change the battery first and then take things from there. They are a chain of stores here in Spain called Norauto so I'm hoping that they won't want any negative publicity. They do tyres, exhausts, car audio etc.