Under EU regulations, passengers are entitled to compensation if delayed by more than three hours when flying from the UK or with an EU airline to an EU airport. Holidaymakers flying short-haul can claim as much as €250, while long-haul passengers could claim up €600 if their flight is delayed by more than four hours.
Compensation claims end up with the CAA if a passenger is dissatisfied with an airline’s decision to reject a claim or has not had a response.
This site has a sample letter you can use to apply for your compensation, under Regulation (EC) 261/2004.
The worst airlines are tracked by the CAA, and a watchdog does monitor them:
Some airlines had an alarmingly high percentage of decisions against
them. Norwegian Air was advised by the CAA to pay up in a staggering
83% of cases. Vueling (79%) and Ryanair (77%) were also told to pay
out to passengers in the vast majority of cases.
The site also lists the airlines by delays, % of complaints upheld, and % of cases where the airline still refused to pay. Surprisingly to me, Emirates did NOT fair well in this list.