My first car had my dad down as a 2nd driver, dropped the premium by a long way. Another way of getting a big discount is getting married! Seriously, a wifey on the policy makes a BIG difference (if you don't mind knackered alloys!)
I can't understand people having their own car but saying it's someone else's main drive. It's the same as not declaring mods (maybe a little less proveable), you get caught out after a major incident then you're not insured...that means car, home and job are all at risk. Is it worth it?