AFAIK you can insure a car registered in someone elses name - however insurer will likely want full details of said person who owns the car (as its their property) & possibly proof of that ownership by way of v5 - i'd guess the insurer would also want to know who else is insured to drive the car on another policy

TBH in the case of an accident i'm not sure how the claim would progress though as technically the vehicle is not your property so could have an affect on payouts, etc