Hi --- If you already have an indemnity policy before building control intervenes or inspects, then that policy will always be in effect. Even if the inspector discovers work is needed at a later date, this is what the policy is intended to cover.
Where you're confused, --- Is once you have already had the intervention of the local building control, you can not then retrospectively apply for one of these indemnity policies, after building control have been involved and brought the matter to your attention.
So in summary --- As long as you have an indemnity in place when you buy the house, any later remedial works found to be required by the building inspector at a later date, would be covered by the policy.