This information is not available.
Complaints about cancellations and delays under Regulation EC261/2004 are handled by the relevant National Enforcement Bodies (NEBs) in the country where the cancellation or delay occurred. Therefore a British national will be in contact with the appropriate NEB rather than the UK Civil Aviation Authority (CAA) if their flight was cancelled or delayed outside the UK. The CAA will handle complaints from British nationals and non British nationals if the cancellation or delay occurred in the UK. The CAA does not record the nationality or residency in all cases.
In addition the CAA will only handle complaints where a passenger has been unable to reach a resolution with an airline and therefore does not have figures for successful cases where the CAA has not been involved.