Deep dive · Updated 08/07/2026
The legal framework: what actually governs the CMS
The CMS is a creature of statute. Every decision it makes must be authorised by an Act of Parliament or regulations made under one — and every decision can be tested against those sources. Knowing the hierarchy is the foundation of every successful challenge.
The hierarchy, top to bottom
Primary legislation
The Child Support Act 1991 is the backbone: it creates the maintenance obligation, the calculation duty (s.11), variations (ss.28A–28G), revisions and supersessions (ss.16–17), appeals (s.20), and the enforcement powers (ss.29–41). It has been heavily amended — always read it "as amended". Key amending Acts: the Child Support Act 1995, the Child Support, Pensions and Social Security Act 2000 (which created the appeal structure), the Child Maintenance and Other Payments Act 2008 (which created the 2012 scheme's gross-income basis and new enforcement powers, some still uncommenced), and the Child Support (Enforcement) Act 2023.
Secondary legislation
The detail lives in statutory instruments, principally the Child Support Maintenance Calculation Regulations 2012 (SI 2012/2677) — income, rates, shared care, variations — plus the Child Support (Management of Payments and Arrears) Regulations 2009, the Child Support Fees Regulations 2014, the Child Support Collection and Enforcement Regulations 1992, and the Social Security and Child Support (Decisions and Appeals) Regulations 1999. The full set is in the legislation library.
Case law
Decisions of the Upper Tribunal (Administrative Appeals Chamber) and higher courts bind the CMS and the First-tier Tribunal on what the legislation means. A decision letter that contradicts a reported UT decision is wrong in law. See the case law digest.
Internal guidance
The CMS works from its published Decision Makers Guide (DMG) and internal procedures. These are not law. The DMG is nonetheless one of the most useful documents a parent can read: it sets out, paragraph by numbered paragraph, exactly what caseworkers are told to do — and this site cites it throughout. But where guidance conflicts with the regulations, the regulations win — a point tribunals accept readily, and one that matters because the DMG is in places narrower than the law it summarises.
The concepts that decide cases
| Concept | Statutory home | Why it matters |
|---|---|---|
| Duty to maintain | CSA 1991, s.1 | Both parents have it; the calculation quantifies the non-resident parent's share |
| Maintenance calculation | CSA 1991, s.11 & Sch 1 | The formula — no discretion in the standard calculation |
| Revision ("look again") | CSA 1991, s.16 | Corrects a decision from its original date — the mechanism behind mandatory reconsideration |
| Supersession ("change it going forward") | CSA 1991, s.17 | Replaces a decision from a new effective date after a change of circumstances |
| Variation | CSA 1991, ss.28A–28G | The only route to add unearned/diverted/notional income or special expenses |
| Appeal | CSA 1991, s.20 | Right of appeal to the First-tier Tribunal after mandatory reconsideration |
| Just and equitable | CSA 1991, s.28F | Variations only granted where just and equitable in all the circumstances — a broad discretion (see PP v SSWP [2022] UKUT 286) |
| Welfare of the child | CSA 1991, s.2 | Must be considered in discretionary decisions (e.g. enforcement choices) — a much-overlooked ground of challenge |
Whether a corrected decision takes effect from the original date (revision) or a later date (supersession) often matters more than the correction itself, because it determines arrears or refunds. If the CMS "fixes" a longstanding error only from today, ask why it is not revising for official error — official error revision has no time limit.
Which scheme are you on?
Three statutory schemes have existed: the 1993 scheme, the 2003 scheme, and the current 2012 ("gross income") scheme. All CSA-era cases have been closed or moved; everything live today runs on the 2012 scheme, and that is all this site covers. Northern Ireland has a parallel scheme with its own legislation administered by the Department for Communities — the rules are similar but not identical, and NI parents should use nidirect.
Sources
| Source | Type | Date | Credibility |
|---|---|---|---|
| Child Support Act 1991 (as amended) | Primary legislation | Current revised text | High |
| CSMC Regulations 2012 | Primary legislation (SI) | Current revised text | High |
| Child Support (Enforcement) Act 2023 | Primary legislation | 2023 | High |
| Commons Library CBP-7770 | Parliamentary briefing | Oct 2025 | High |
| PP v SSWP (CSM) [2022] UKUT 286 (AAC) | Case law | 2022 | High |