HC Deb 10 December 1958 vol 597 c56W
44. Mr. Page

asked the Postmaster- General upon what principles or definition a decision is made as to whether a card contains a conventional greeting, when the postage is 2d., or a message, when the postage is 2½d.; and who makes the decision.

Mr. K. Thompson

Broadly, the distinction is between messages which give or ask for information and formulas of a conventional kind which do not. "Arrived safely. Weather shocking." costs 2½d. but "Greetings to all in Walton" goes for 2d. The decision is taken by sorting office staff, who are provided with printed official guidance.