A lot of the recipes from the 1942 recipe book use Yeastrel which is no longer manufactured.
Yeastrel “The Vitamin B Savoury” first appeared sometime in the early 1930’s and was a yeast extract produced by a firm in Fountainbridge, Edinburgh Scotland. It was claimed to be a rich source of vitamin B and was used as a food supplement during the war being sold through health food stores.
Production continued until sometime in the mid 1960’s. The product was still being advertised in 1962/63.
The nearest equivalent we have today is Vegemite™ which is produced by Craft Foods in Australia although it widely available in the United Kingdom. Yeastrel may have been less salty then Vegemite™ so if you are using this as a substitute you may need to use less than the recipe amount.
I you remember this product and can add to this information, please get in touch.