I have received a protest in regard to this matter and would like to express my regret for any inconvenience caused. Air exercises, arranged in conjunction with local authorities and anti-aircraft commanders, took place in certain districts on the 13th and 14th July and there was low cloud and poor visibility in the neighbourhood of Sheffield. It has not been possible to identify the aircraft concerned from the particulars furnished, but it is probable that the pilot was forced by the weather conditions to fly low. Every effort is made to avoid unnecessary risk or annoyance.