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Milk For Spain was a fund-raising campaign during the Spanish Civil War (1936 - 1939) set up by activists in the Co-operative Union and the Labour Party. It received donations from co-operative societies, and customers could contribute money buying tokens. Advert is from the M&S (Manchester & Salford) Co-operative Herald November 1938 promoting the scheme. The milk in powdered or condensed form was sent from Britain to the Spanish Republican areas.
Wikipedia - Link.