Deadlock letter

A deadlock letter is a letter or email in which a company says it cannot do anything more to resolve your complaint. Energy and telecoms firms use the name; banks and other financial firms call it a final response.

The letter matters because it starts the ombudsman clock early. The rules checked on 27 September 2026:

• Energy: according to the Energy Ombudsman, your supplier has 8 weeks to resolve a dispute unless it sends a deadlock letter first, and you must bring your case within 12 months of receiving the letter.
• Financial services: under the FCA's DISP 1.6 rules, a firm must send a final response within 8 weeks (15 business days for payment services complaints), and the Financial Ombudsman Service says you then have 6 months from its date to refer the complaint.

Example: you complain to your energy supplier about a £420 back-bill on 1 August 2026. It sends a deadlock letter on 20 August 2026. You can go to the Energy Ombudsman the same day rather than waiting until 26 September 2026, and your last day to do so is 20 August 2027.

Ask for a deadlock letter in writing if talks stall. Find the right ombudsman and your deadline with the complaint route finder.