I have held full uk driving license for 30 years and am in the process of exchanging it for a Spanish one. Given that almost all car rental companies require you to have held your license for at least a year, when I receive my new Spanish license can I use it to hire a car in the uk immediately or will I have to wait a year?
I exchanged my British driving licence for a Spanish one in 2012. Unlike the British licence, the Spanish one doesn't have a counterpart: all the information on validity is on the plastic card. This includes a table on the back showing your entitlements. Mine shows class B valid from the date I passed my test in the UK (in 2003). It also has an "Observations" field with a code which says that my original licence was from the UK.
Note that you may lose special entitlements. My UK licence had a ton of special classes, but my Spanish one only has class B. Still, that's what matters for hiring a car.
As per this article from an automobile magazine, you will probably get a license with an special code with key 106.3 with the first issuance date, so you should be able to provide proof of experience.
I'm not sure if this code is a national code or a EU-wide code, though.