Friend has lost an earing of significant value, unknown where exactly. The insurance company will want a reference number to show it has been reported to the Police but to which Police do we report it, local, guardia or nacional or will any of them take the report. Will I have to report it to the station in charge of where they are staying? I would rather know first rather than spending the day driving from one station to the other as they all just send you on to a different place rather than actually deal with you!

I, personally, would go to the local first but they may pass you on to the national police. Do it where they were staying.

Start with the local police if you need an official report.

Some towns have an "oficina de objetos perdidos" where they keep items found.

The Police local were very helpful when my wife lost her handbag. If you do not speak spanish take someone who does.