Up until fairly recently, nearly all insurance policies (whether 'fully comp' or just 'third party') provided cover for driving another person's car (with third party cover only). Some policies included a specific exemption, stating that the insurance didn't cover the driver using the car of a close relative or of another person living at the same address.
However, many insurance companies have now removed this 'third party - any vehicle' cover from their policies.
Driving without valid insurance can either be dealt with by a fixed penalty or through the courts. The fixed penalty is a �200 fine and 6 points on the licence. In a court, the maximum fine is �5000, plus 6 to 8 points on the licence. (The court may also impose an immediate driving ban. This is unlikely but it's different to the licence revocation, referred to below, in that a ban is for a fixed period of time but 'revocation' allows the driver to take to the road, as a learner, as soon as he's got a new provisional licence).
It's also an offence to 'cause or permit' another person to drive a motor vehicle without insurance. So it's possible that the driver's father may also face prosecution. (The same penalties apply upon conviction).
When someone, who has passed their test within the past two years, reaches 6 points on their licence, that licence is automatically revoked. There is no appeal against this procedure. The driver has to apply for a new provisional licence and book another driving test.
Chris