Wikipedia tells us that the first loaf–at–a–time bread slicing machine was invented in 1912 by the American engineer Otto Rohwedder. Born in 1880 in Davenport, Iowa, Rohwedder had by this time settled in St. Joseph, Missouri. His prototype was destroyed in a fire in 1917, and it wasn't until 1927 that he had a working machine; but this one didn't just slice the bread, it wrapped it as well. Rohwedder sold the first machine to the Chillicothe Baking Company in Chillicothe, Missouri (74 miles from St. Joseph), and the first sliced loaf was sold on 7 July 1928.
The second machine was sold to Gustav Papendick, a baker in St. Louis, Missouri, who improved its wrapping capabilities. By 1933 more than 50% of the loaves being sold in the USA were sliced, and in the same year Rohwedder sold his patent rights to a company in Bettendorf, Iowa (a suburb of his home town of Davenport). He then joined that company, becoming vice–president and sales manager of the Rohwedder Bakery Machine Division. He retired in 1951, and died in 1960 aged 80.
In 1940, a product consisting of two wrapped half–loaves was advertised in Danville, Virginia (and possibly elsewhere) as the "greatest convenience since sliced bread". This may well be the origin of the well–known phrase "the best thing since sliced bread".
In 1943 sliced bread was banned in the USA, on the grounds that it required heavier wrapping than unsliced and to counteract a rise in the price of bread (resulting from an increase in the price of flour). There was a public outcry, and the ban was rescinded after less than two months.
According to a letter published in the Daily Telegraph in 2011, "the first bread slicing and wrapping machine was installed in the Wonderloaf Bakery in Tottenham, in 1937, having been patented in America in 1934. The war slowed things down a bit, but by the 1950s, the sliced loaf accounted for 80 per cent of the bread market in Britain." This was in response to an article claiming that sliced and wrapped bread was introduced to Britain in 1961, at the same time as the Chorleywood Bread Process (which allows bread to be made from lower-protein wheat, and in a shorter time, in comparison to traditional methods; it was said to account for 80% of UK bread production in 2009.)
Another Telegraph correspondent, at the same time as the first, recalled "unwrapping hundreds of loaves of sliced bread as a fatigue occupation at RAF Padgate in September, 1952 ... we had to make sure not to rip the paper, as it would be used again for wrapping sandwiches."
So, to summarise: sliced bread was first sold in the USA in the 1920s, and in the UK in the 1930s (probably). (Is it just me that wishes UK question setters would indicate whether they mean a worldwide first or a UK first?)
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