The question of driving experience is vaguely covered by your NCB.
I agree it's a bit silly that you can get your licence, not drive for say 5 years and come out to lower premiums despite never actually driving since your driving test.
It's kinda hard to verify driving experience really. How can you actually verify the mileage someone has done? Go by the mileage reports on MOT certs? But what about miles racked up in other vehicles? What if you're a HGV driver? You can be looking at 50,000 -100,000 miles a year right there. What about experience with other vehicles such as MHE (PPTs, Forklifts, etc... (More experience in tighter areas, theoretically less likely to have a low-speed shunt in a car park for example))? They don't usually record mileage, only hours.
It's just not practical to verify that sort of thing, so they assume that you've been driving the duration you've had your licence. That's where questions about NCBs, driving offences and accidents come in.