Car insurance - extra premium for learner?

[fadingfast]

We have two cars, insured under a joint policy with LV (cost for each is quoted separately). On our smaller/cheaper car, we added my son last year as he is leaning to drive, so obviously that added to the cost of insuring that car by quite a lot.

Renewal quote came though recently, and the quote for the other car has increased by 30% from last year. LV couldn’t explain why. We’ve now taken DS off the policy completely, reducing the premium by more than half. What I don’t understand is that the premium for the car that he wasn’t insured on has also reduced significantly, because he’s no longer insured to drive the other car. This makes no sense to me and the person at LV couldn’t explain why either. Does anyone understand why??

There was a thread yesterday talking about how much insurance premiums this year, my own renewal was quoted at £200 more than last year but I got that down to £100 increase by shopping around.

Yes I realise shopping around will help but I just don’t understand why the cost of insuring car 2 has increased just because we were insuring DS to drive car 1. It’s definitely because of him that the premium for both cars went up, even though he’s only a named driver on one of them! Seems very wrong to me.