Even if downloading it for the purpose of having a backup is your goal, it's still piracy in the UK and the US. There is no difference.
Fair use means you are allowed to make a copy of your OWN legally owned/purchased copy. But if the only copy is on a digital platform, then you aren't allowed to have a pirated copy as a backup measure.
You can disagree with me if you want to, but them's the legality of it.
