From the War Cabinet minutes 6th September 1939 :
6. The Secretary of State for Air explained the reasons why an air raid warning had been issued in the early morning of 6 September.
The question of a communiqué was discussed. It was agreed not to issue one at the moment, but the Secretary of State should have discretion to issue one later if necessary.
7. The First Lord of the Admiralty reported that five merchant ships, four British and one French, had been sunk by submarine the previous day. There was reason to believe that the position from our point of view was probably now at its worst and would improve.
Rigorous steps were being taken to ensure that merchant ship captains obeyed the instructions given them.
Two German merchant ships had been sunk by H. M. S. Ajax on the previous day. The sinking had been in accordance with the rules of war, but it was not clear why H. M. S. Ajax had been unable to find prize crews and take the ships into port. The Admiralty would take steps to ensure that wherever possible enemy merchant ships were captured and not sunk.
8. The Chief of the Imperial General Staff gave an account of the situation in Poland, which had deteriorated very rapidly. Information was very meagre, but the Polish army still appeared to be intact.