Such difficulties as these will, sooner or later, have to be faced; but at present there are in existence only the simplest of laws, and these have been framed for the safety of the public, and to protect strategical areas from the attentions of foreign spies. Flying over towns is--as has been stated--declared a dangerous practice, and is no longer allowed; while the officials of our Home Office, after consultation with the naval and military authorities, have imposed restrictions upon the entry into this country of foreign craft. A machine reaching our shores from abroad can only land, for instance, between the points specified below, and outlined upon Fig. 103, and then only after its pilot has given eighteen hours’ notice to the Home Office, either by letter or telegram, of his intended flight:[3] Fraserburgh and Ythan River. Holy Island „ Newbiggin. Sutton (Lincolnshire) „ Holkham (Norfolk). Stansgate Abbey „ Burnham-on-Crouch. (on the Blackwater) Margate „ Walmer. Rye „ Eastbourne. Hove „ Bognor. Bridport „ Dawlish. It is declared unlawful for an aircraft entering England from abroad to carry any goods upon which Customs duty is payable, or the importation of which is prohibited by law; any photographic apparatus, carrier pigeons, explosives, or firearms, or any mails. Upon arrival in one of the landing areas prescribed, the airman fills up an official report, and obtains a permit which allows him to continue his flight inland. Before leaving the country, upon his return abroad, he must alight in one of the coastal areas. No exemptions are granted to these rules unless by the authority of the Home Office, and no foreign naval and military aircraft are permitted to fly over or land in England unless upon a Government invitation. A number of points in the United Kingdom have been specified over which, for strategical reasons, no flying is permitted--although such rules do not apply of course to British naval and military craft. The mouth of the Thames is closed to aviation; fortifications like those at Dover are declared out of bounds; also dock-yards such as that at Portsmouth. The question arises naturally: how are these rules to be enforced? What is to prevent an aircraft infringing them? By the Act of Parliament in which they are set forth, there is a clause which reads: