The Child Maintenance Service (or, for existing cases only, the Child Support Agency) determines the minimum amount a non-resident parent must pay towards the care of his/her children. If a court rules that a higher payment is appropriate (because, for example, the non-resident parent is a billionaire and it was his/her fault that the relationship broke down) then the CMS/CSA calculation becomes irrelevant. (The same will apply if there's no court ruling but the parents simply agree on a settlement).