Whilst the International Certificate of Insurance or Green Card is routinely issued with motor insurance policies in Gibraltar, the prospect of a “no deal” Brexit will actually mean that the Green Card is a legal requirement for driving a Gibraltar registered/insured vehicle in Spain and the rest of the EEA. Similarly Spanish registered/insured vehicles will als require a green card in order to remain legal in Gibraltar.
An agreement was reached in May 2018 that this requirement should be waived following the UK’s exit from the EU but that agreement has not yet been ratified by the European Commission.
In the absence of that or any other agreement you will need a green card to drive your vehicle and tow any trailer in Spain or the rest of the EEA. Failure to present one upon request may lead to prosecution, a fine and possible seizure of your vehicle.
Whilst green cards are generally issued it is essential that you carry it with you when driving in Spain and make sure that if you are towing a trailer, caravan etc it is either noted on your annual green card or that you hold a separate green card for the trailer.
There is also some misinformation about the standard European Accident Report form. This is not a legal requirement in Spain or the rest of Europe, but it is extremely advisable to carry one with you you to ensure that you correct adequate and correct information for your own protection.