Hi Barry,
You'll probably find that whilst Key Care is part of a motor/home Insurance package it is usually a separate policy Underwritten by an alternative Underwriter.
It would be worth checking this out as if the key care is independent of your Motor Underwriter it will probably have a smaller excess and would NOT impact the Motor policy NCB.
If you've key cover with Greenlight under Boomerang key cover I can confirm that when claiming under key care you would not impact your motor policy NCB.
Kind regards & hope this helps
Tony