You’re right about the named drivers boys, but I’ll give you the flip side, when I asked to add him to his sisters policy, (she was 18) it doubled.
They reckoned with two inexperienced drivers sharing, a bash is guaranteed laugh2

Everything is with Aviva under one principal policy, however, they both are treated as having their own policy and anything they do doesn’t affect my policies.

I could earn a bit more discount if I could be bothered to use the App, you drive properly for 200 miles ( of your own choosing), and an extra discount is applied on renewal.
It only applies to any car where I’m the main driver though, so not much of a saving really.
The other handy thing with Aviva, if you’re daft enough to have extra cars like me, you can take one off the road and substitute it for another with no admin charge and each car premium is calculated to the day, so no money is wasted.

Strangely, the only one they don’t like is the caterham, the least valuable and only 150hp!