The impact of World War II on metal requirements and availability led to some changes in coinage alloys in 1942 (and even experiments with "the new plastic materials to save metal"). The mint reported "As the Japanese invasion threatened a substantial portion of the world's tin supply, consideration was given to methods of reducing the Mint's requirements of that metal for coinage". For many countries that employed the Royal Mint, London for their coinage needs, the bronze issues were changed to a new alloy containing 0.5% tin. At the same time nickel was becoming an important war effort material; some countries changed their cupro-nickel coinages for the new bronze alloy while for British Honduras the change was to a nickel brass alloy of 79% copper, 20% zinc and 1% nickel.
The Royal Mint Record coin was not struck at the usual high proof level (compared with the 1949 Proof of Record issue for example). It is however a special strike, a specimen or lower mirror finished proof - a reflection of the needs of the war effort.
References to original information:
Seventy-Third Annual Report of the Deputy Master and Comptroller of the Royal Mint, 1942, p.122 and 131.