Child Support Act 1991, ss 96B, 96F, 104
In general, you must apply first to Inland Revenue. You can apply to the Family Court for a departure order only if:
Inland Revenue has already made a decision on your application for a departure from the formula assessment, or has refused to make a decision because it thinks the issues are too complex and should be left to the Family Court, or
either or both parents are already involved in another case that’s going to be heard by the Family Court, and it’s appropriate for the departure application to be heard along with that other case.