How to write a complaint letter that works

The structure that works

Six elements, in this order:

1. The subject line. Write "Formal complaint" or "Complaint" so the company's system routes it correctly.
2. Your account or reference. Make it easy for the agent to find you in their system.
3. What happened. Two or three sentences of fact, dated, with no editorialising. "On 4 March 2026 my flight LH123 from Heathrow to Berlin was delayed by 4 hours and 25 minutes."
4. Why this is their problem. Cite the scheme or law concisely. "Under UK261 / Regulation (EC) 261/2004, a delay of more than three hours on a flight of this distance entitles me to £350 in compensation."
5. What you want. Specific. "Please credit my account with £350 within 14 days."
6. What you will do if you do not get it. Name the ombudsman. "If I have not received a response by 12 May 2026, I will refer this to the Civil Aviation Authority and to a small claims court."

A copyable template

Which ombudsman to name

Picking the right ombudsman matters. Companies dismiss a wrong-ombudsman threat. Pick from this list:

• Financial services (banks, insurance, motor finance, credit cards): Financial Ombudsman Service.
• Energy (electricity, gas suppliers): Energy Ombudsman.
• Water: Consumer Council for Water.
• Phone, broadband and TV: one of two schemes, and which one depends entirely on your provider rather than on what you are complaining about. BT, EE and Plusnet go to the Communications Ombudsman; Sky, TalkTalk, Virgin Media, Vodafone, Three and O2 go to CISAS. Getting this wrong costs weeks, so check yours against the full provider list, which also covers the six week rule that replaced the old eight week wait in April 2026.
• Trains (operator first, then) Transport Focus (national rail) or London TravelWatch (London).
• Flights: CAA Passenger Advice and Complaints Team, or the airline's named ADR (CEDR for many UK and EU carriers).
• Council services: Local Government and Social Care Ombudsman (England), Public Services Ombudsman (Wales / Scotland / NI).
• Housing (private renters): First-tier Tribunal, or the Property Ombudsman if your landlord uses an agent registered with them.
• General consumer (retail, services): Citizens Advice consumer service, then Trading Standards.

Common mistakes that kill the response

• Anger without specifics. "This is unacceptable" without "on 4 March, ticket reference XYZ" is easier to dismiss.
• No reference to a scheme or rule. "Compensate me" works less well than "compensate me under UK261".
• No deadline. Without a date, the letter sits in a queue indefinitely.
• Multiple complaints in one letter. Send one letter per issue. They get logged separately and routed differently.
• Naming the wrong ombudsman. Companies notice and adjust how seriously they take you accordingly.
• Forgetting to keep a copy. Save the email chain or a copy of the posted letter. The trail matters later.

When the first letter does not work

Most letters get a response within the 14 days. If yours does not:

1. Send a brief follow-up after the deadline lapses. "I have not received a response. I am escalating to [ombudsman] today." This often produces a response within 24 hours; companies process the file at the threat of escalation.
2. File with the relevant ombudsman or regulator. Their forms are short and online. Decisions take six to ten weeks typically.
3. For financial sums up to £100,000 with no ombudsman route, or where the ombudsman's decision was rejected, file at Money Claim Online. The fee is £35 to £455 depending on the amount, claimable back if you win.

How Untap helps

For the four recurring categories Untap automates (trains, flights, parking, TfL), we draft the appropriate letter for you and you send it. For one-off categories Nell, our voice agent, walks through the question set and drafts the letter you need (deposit, motor finance, broadband, smart meter). We never send on your behalf and we never take a cut. The letter is yours; we just make the structure quicker.

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