Re: Here in Belgium...
"something to convince the military police (carabinieri), flying squad (pol-strada), police (polizia), local police (polizia locali, urbani, regionali, communale), tax-police (guardia di finanza) and forest police (really), any whom of which might demand WHY you are outside the home region?"
As a fellow Italo-Brit I have to say that you forgot the polizia penitenziaria, the polizia postale and the vigili urbani. No doubt there are many others.
Due to an unfortunate decision to return to the UK to cope with family matters I'm now stuck in the septic isle unable to drive home. I'm getting to the point where I'm tempted to issue a certificate from my own company declaring that I'm a courier, complete the paperwork for France and Italy and drive home delivering essential agricultural supplies.