No, you don’t have to be the car’s registered keeper to be the main driver on your car insurance. But the registered keeper does need to be a named driver on the policy.
The main driver is the person who uses the car most often and it’s important your policy accurately reflect this.
Falsely naming a more experienced driver as the main driver on your insurance to get a lower premium is called fronting, which is a type of insurance fraud. In other words, it’s illegal and could invalidate your insurance leaving you to foot the bill in the event of a claim.
The consequences of fronting don’t end there, though. You could also be taken to court, charged, and end up with a criminal record.