If you have already filed a formal complaint with a UK-based airline and are unsatisfied with their response after 8 weeks, you can escalate the matter to an Alternative Dispute Resolution (ADR) body or the Civil Aviation Authority (CAA). Most major UK airlines, such as British Airways and easyJet, are members of an independent ADR scheme (like CEDR or NetJets) which provides a legally binding decision on your claim. You can find out which ADR your airline belongs to by checking their website or the CAA’s official list. If the airline is not a member of an ADR, you can submit your case to the CAA’s Passenger Advice and Complaints Team (PACT). When escalating, ensure you have a "Deadlock Letter" from the airline or proof that 8 weeks have passed without a resolution. Be prepared to provide copies of all correspondence, flight details, and receipts for any out-of-pocket expenses. This process is generally free for the consumer and is the most effective way to secure compensation for delays, cancellations, or lost baggage under UK261 regulations.