Yes, yes, you're allowed to post links to information that would be helpful to other travelers. Please do.

Sorry for my ignorance, but as I live in the US, I'm not familiar with the Guardian, etc.

Have you used this 3rd party insurance before? I've rented many cars while traveling in England, and (maybe incorrectly) thought that I was covered for damage to the rental car by my credit card's insurance. I always decline Collision Damage Waiver, etc. Thankfully I've never had a crash, but if it's the smart thing to get additional insurance when I rent there, I'd like to know.

Thanks a lot for your info.