You keep the NCB because you haven’t claimed on that policy however you’re insurance premiums will go up.
I have a car policy with 10 years NCB and made a claim on the bike policy. Lost the NCB on the bike policy obviously and had to declare the claim on the car policy. End result I still get 10 years NCB on the car policy but the premium has gone up due to the claim on the other policy and therefore greater risk.
Also of interest a lad at work had an own fault accident in the works van, he never lost his NCB on his private car policy but the premium went up considerably due to the claim on the works policy.
Because of they way the insurance companies work and share their databases you have to declare all accident claims regardless of which policy they were on, failing to do so could result in being uninsured.
Reminds me of my younger sister years back, long story short
16th birthday, first bike, first day on the road, single handed caused multicar RTA. She inadvertently pulled a wheelie and slid off the back, sat in the road and watched her Cub bounce from car to car and the cars shunted into each other like an American OTT film set. Five cars were written off and a dozen or more were damaged. Her insurance premiums looked more like telephone numbers for the next 5 years.