Assuming you have a valid driver's license...
In the scenario that you get stopped at a police roadblock, it
doesn't matter to the police whether the car belongs to you or not.
Even the presence of your friend doesn't matter. Unless of course
you caught for drink driving, then that is confirm deep sh!t.
In the scenario that you get into car accident with another
vehicle, insurance will not cover you( even if it was not your
fault), so you must pay your friend's mum the repair costs.