The aircraft was undertaking target towing operations for a military exercise and was recovering the target whilst flying in an assigned danger area over the English Channel. With the target approximately 40 m from the aircraft, the target winch accelerated rapidly and the target struck the leading edge of the wing before detaching and travelling over the wing. Although, the launcher and the droop leading edge on the wing were damaged, the aircraft landed safely. The target winch is powered by a turbine, and the speed of the turbine is controlled by vent doors. The target winch had oversped due to a fault with the closed limit switch on the vent doors which prevented the doors from closing. The operator and manufacturer have carried out several safety actions as a result of the investigations and one Safety Recommendation is made.