Airmail
BALDWIN, N. C. Heliposts. Sutton Coldfield: Francis J. Field, 1954(?). 12 pp.CHAMPNESS, M. V. D. East Anglian Helicopter Mails. Bishops Stortford: East Anglia Postal History Study Circle, 1973. 38 pp.
NEWALL, Alexander S. British External Airmails until 1934. 2nd edn. London: Christie's Robson Lowe, 1996. 425 pp.
REDGROVE, H. Stanley. The Air Mails of the British Isles. The story of the development from the venture of the Great Western Railway in 1933 to the outbreak of war with Germany. Privately printed, 1940. 150 pp.