The term Black Market was particularly used during World War II in Britain to refer to the underground/illegal network where anything could be obtained for a price.
Rationing was introduced during the war for many items including meat, cheese, butter, sugar, clothing, and petrol. If they didn't have the coupons then people would often resort to the local black marketeer. Though frowned upon people often found them useful and so they were tolerated.
Some Rationing continued into the mid 50's in the UK and is one of the topics lampooned in the 1949 British movie "Passport to Pimlico". Also Private Walker in Dad's Army
is portrayed as a sympathetic black marketeer.