England. Cabinet Office
Her Majesty's Stationery Office, 1988
Buku Referensi
England. Cabinet Office
Her Majesty's Stationery Office, 1989
Buku Referensi
Encyclopaedia Britannica Inc., 1988
Buku Referensi
ICAO , 1988
Buku Teks
London Guinnes Books 1987
Buku Referensi