Five catalogues have been published about British Postal Orders and all are still relevant and available from the Society
History and Values of British Postal Orders 1881 -1984 by Howard Lunn (1985) This is an A5-ish sized hardback containg 64pp. Eight pages are devoted to the history of the Postal Order which wase introduced as a viable alternative to the Money Order. There are illustrations of every separate issue up to 1984 and suggested prices. Some prices are a little out-of-date, but nevertheless a good starting point. Well worth obtaining for reference.
The Standard Catalogue of Postal Orders Vol.I (The British Postal Order 1881 - 1981) (1985) by Stephen Cribb. Card cover with 66pp and slightly larger than A5. Four pages introduce the subject and every denomination issued is listed. Here again and attempt is made to price each issue. Also worth purchasing. No further volumes were added. Now sold out, but often sold on eBay.
Promotional Postal Orders by Howard Lunn (1995) In this publication Howard lists these orders issued from Cinzano in 1984 to General Guarantee in 1995 nearly 50 in total. 49pp with an illustration of every type. The Postal Orders were mostly received as a refund from an offer involving several purchases and returning labels, bottle tops, proofs of purchase, etc. Howard obtained many of these items personally, directly from the manufacturers as some of those issued were very difficult to acquire.
British Postal Orders 1881 to 2005 by Michael Brill (2005) this is the latest definitive publication on the British issues, still obtainable from the Society priced £10 post free. Comprises 88pp A4. A useful update was published in the Postal Order News in July 2007.
Our latest catalogue published in conjunction with the GB Overprints Society is a Directory of Overprinted British Postal Orders by John Gledhill. Published in March 2010 and priced £10 plus postage.
Other catalogues which may be of interest are :-
The Canadian Revenue Stamp Catalogue 1991 ESJ Van Dam Inc. Postal Note stamps and Postal Scrip stamps
Catalogo De Enteros Postales Argentinos 1991 Inc. Bonos Postales
Catalogue Generale Postali D’Italia 1970 Inc. Vaglia
Die Posttaxen der Schweiz from 1875 (1995) Inc. Mandats and Postanweisungen
Postanweisungen Ganzachen – Katalogue Deutschland (1972) Michel
Green Papers 38A Postal Orders 1938 and 42A International Postal Service
Il Nuovo Pertile 1991 Italian Specialised Catalogue Inc. Listing of the Cartolina Vaglia
Introduction and Usage of Postal Orders in Bechuanaland Peter Thy (1994)
Les Entiers Postaux de France Storch (1992) Inc. Bons de Poste
New Zealand Postal Notes 1886-1986 Jack Harwood 2010
The Postal Commission Stamps of Ceylon 1888-1890 JG Winters
Queensland Postal Notes (2004) Dave Elsmore
Speciale Catalogues (Netherlands) 1954, 1966 and 1969. Inc. 1884 Money Order stamps
Standard Catalogue of World Paper Money Specialized Issues 6th Edn. Vol.One Albert Pick. Lists the Orange Free State and ZAR Postal Orders
The Canadian Revenue Stamp Catalogue 1991 ESJ Van Dam Inc. Postal Note stamps and Postal Scrip stamps.
Directory of Overprinted British Postal Orders by Dr JM Gledhill
Postal Orders and Savings Certificates of Pakistan and British India
Guezendam's Catalogue van de Postwaardestukken van Netherlands, which includes the Postbewijs (money orders)