Enemy Aliens. Memo. By Director of Intelligence, Air Ministry

(d) This country will have to face for an indefinite period the threat of invasion. In such circumstances national security must surely Outweigh every other consideration. (e) The enemy have been planning for this war for upwards of 10 years many people think even longer and they have been thorough in their preparations. It would be an elementary precaution on their part to ensure that Agents planted in this country should have a record of long residence and outward friendliness. (f) There is evidence that of recent months the Germans have been troubled by a marked diminution in the amount of information derived from this country.