Know Your Rights
How to formally complain to CMS — step by step
The CMS complaints process is not straightforward. ICE will not get involved until CMS has issued a final response — which may never come. Follow this guide exactly, in order, and keep a record of everything.
Child Maintenance Service
Steps 1 & 2 — Send complaints here
Child Maintenance Service
Mail Handling Site A
Wolverhampton
WV98 2BU
Telephone: 0800 171 2345
Textphone: 0800 735 7699
Web: gov.uk/child-maintenance-service
Always send by Royal Mail Tracked 24 or Special Delivery and keep your receipt. Keep copies of everything.
Independent Case Examiner (ICE)
Step 5 — Only after CMS issues a final response
The Independent Case Examiner
PO Box 209
Bootle
L20 7WA
Telephone: 0800 414 8529
Email: ice@dwp.gov.uk
Web: gov.uk/independent-case-examiner
ICE will only accept your case after CMS has issued a final response to your complaint — or after you have exhausted all other steps below. Do not contact ICE until you have been through the full process.
Write a clear, formal complaint letter. Be specific — include dates, reference numbers, payment amounts, and names of any CMS agents. Do not rely on phone calls. This letter starts your official 40-working-day clock.
Important: Send by Royal Mail Tracked 24 or Special Delivery. If CMS claims they never received your letter, your proof of postage is your only protection.
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Complaint Letter Template 1 — Registered Supporters Only
Ready-to-personalise Word document available exclusively to registered supporters. Free to join.
CMS should acknowledge within 5 working days. If you've heard nothing by Day 7, send a chaser immediately. This creates a second paper trail entry. Do not wait — every day lost counts against your 40-working-day window.
Tip: Check your Royal Mail tracking reference before sending. Include the tracking number in the chaser letter.
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Chaser Letter Template — Registered Supporters Only
Access this and all letter templates in the supporter library.
If you have not received a full response from CMS within 40 working days, your next step is not ICE — it is your MP. ICE will not accept your case until CMS has issued a final response or the process has been fully exhausted. Your MP can intervene directly with DWP ministers and request that your case is urgently reviewed.
Important: Do not go to ICE yet. ICE requires a final CMS response before they can accept your referral. Going to your MP first is faster and more effective at this stage.
What to say to your MP: Write formally explaining that you submitted a complaint to CMS on [date], sent by tracked post (include your tracking number and delivery confirmation), and that CMS has failed to respond within the statutory 40 working days. Ask your MP to contact DWP directly on your behalf and request an urgent response. Use our
MP letter template in the supporter library.
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MP Letter Template — Registered Supporters Only
Ready-to-personalise Word document covering your personal case, the five reform points, and specific parliamentary questions for your MP to submit. Available exclusively in the supporter library.
While waiting for your MP to respond, continue chasing CMS directly by both phone and letter. The goal is to establish on record that CMS has received your complaint, to find out who your case worker is, and to create a documented timeline of every contact attempt.
What to ask CMS when you call:
• Has my formal complaint dated [date] been logged on the system?
• Can you confirm receipt of my letter sent by tracked post, reference [tracking number]?
• Who is the case worker assigned to my complaint?
• When can I expect a response?
Stay calm and be polite. The call handler answering your call did not create this situation. They are working within a broken system. Being polite costs nothing and will always serve you better — note the name of the agent and the date and time of every call.
💡 While you wait — submit a Subject Access Request
While chasing CMS by phone and letter, submit a SAR to DWP. Your SAR will reveal what's actually been recorded on your case — call notes, internal comments, calculation records — which may directly support your complaint.
Read the full SAR guide →
After every call, every letter sent, and every letter received — write it down immediately. Date, time, who you spoke to, what was said, what was promised. This log is your most valuable asset if this ever reaches ICE, the Ombudsman, or Parliament.
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Case Timeline & Evidence Log Template — Registered Supporters Only
A comprehensive Word document template to record every event in your case — chronological timeline, payment analysis, grounds of complaint, call log, evidence checklist, and outcomes sought. Keep it updated throughout your case and attach it to every escalation letter you send.
When CMS finally issues a final response to your complaint — whether that takes 40 days or considerably longer — and you are not satisfied with that response, you can now refer your case to the Independent Case Examiner. ICE is independent of CMS and DWP and can investigate maladministration, recommend financial redress, and require CMS to take corrective action.
ICE will not accept your case without a final CMS response. If CMS has still not responded at all, continue pursuing via your MP (Step 3) and direct chasing (Step 4) until you receive one.
What ICE can investigate: Delays, errors, maladministration, poor service, and incorrect calculations. They can recommend apology, compensation, revision of a decision, or corrective action. CMS must respond formally to every ICE recommendation. ICE is free to use.
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ICE Referral Letter Template — Registered Supporters Only
Full ICE referral template with investigation requests, remedies to seek, and a documents checklist.
If ICE does not resolve your case satisfactorily, go back to your MP and ask them to refer your case to the Parliamentary and Health Service Ombudsman (PHSO). You cannot approach the PHSO directly — it must be referred by an MP. This is the highest level of escalation short of judicial review.
Parliamentary and Health Service Ombudsman: Millbank Tower, 30 Millbank, London, SW1P 4QP · 0345 015 4033 · phso.org.uk
At this stage, write to your MP again summarising the entire timeline — your original complaint, the CMS failure to respond, the ICE referral and outcome, and why you believe the Ombudsman must now investigate. Attach your full case log. Your MP will be far more likely to act if you present a clear, organised, documented case.