31.This paragraph provides the rules for determining which non-resident parents will have a flat rate liability.
Sub-paragraph (1) provides for the flat rate to apply where the non-resident parent has net weekly income of £100 or less; or he is in receipt of a prescribed social security benefit, pension or allowance, or he or his partner (if any) is in receipt of prescribed benefits.  The flat rate is not payable in a case where a non-resident parent has a nil liability (see paragraph 5).
Sub-paragraph (2) provides for the flat rate to be payable at a different amount where the non-resident parent has one or more partners who are also liable to pay child support, and either the non-resident parent or his partner is in receipt of a prescribed benefit (intended to be Income Support or income-based Jobseeker’s Allowance).  For example, in a case where both members of a couple in receipt of Income Support are non-resident parents, it is intended to provide for the non-resident parent’s liability to be one half of the flat rate amount.
Sub-paragraph (3) provides for the prescribed social security benefits, pensions and allowances in sub-paragraph (1)(b) to include those paid to non-resident parents under the law of countries other than those in the United Kingdom, for example a state retirement pension paid to an EU national.
Part 1: Child Support. Commentary on Sections Schedule 1: Calculation of weekly amount of child support maintenance Paragraph 4: Flat rate