If you are the owner of a car that has been caught speeding in Spain you will receive a letter with a requirement to identify the driver and some details of the offence. Individuals can choose to pay the fine straight away, unless they are Spanish residents and the driver identification is mandatory (fines with points deduction). Companies will usually choose to identify the employee / client who was driving. Here is a sample identification form that might be useful (I have omitted the head). I would attach a copy of the driver's driving license and fax it to the 0034902512151 (yes, they still use a fax).
Driver identification
Dossier: 111111111111
The driver at the time of the offence was,
Name: Mr. John Smith
Birth date: DD/MM/YYYY
Driving license nr:
Address: 123 Street
Hereandthere
A12 34B Charming Village
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You can also fax a copy of the requirement, though the dossier or expediente number is the only thing they need.