Andorra is a separate state I believe. Many UK insurance policies do not cover Andorra, but many do. Always worth checking.I've driven to Andorra several times never thought about a green card. I did it once in a hire car from Spain I was only asked if I would be leaving Spain not if I was going to Andorra or France.
Not our experience at all, we've been a few times, whilst the wine isn't cheap the spirits certainly are! The scenery going northwards to France is absolutely fantastic.Wouldn't go through Andorra anyway it is just one long traffic jam, also nearly got really overcharged for wine in a supermarket there