“The majority of shoppers find it easier to spread jam, or their preferred filling, on a straighter shape with a single sweeping motion,” he said in a statement. “With the crescent-shaped croissants, it’s more fiddly, and most people can take up to three attempts to achieve perfect coverage, which increases the potential for accidents involving sticky fingers and tables.”

But in a week when Prime Minister David Cameron was in Brussels trying to wring concessions from fellow European Union leaders over Britain’s future in the 28-member bloc, The Times of London called the timing of the “major culinary snub” to the quintessentially French pastry “indelicate to say the least.”

Still, for all the fuss about breaching French tradition, Benjamin Turquier, who beat 149 other contestants last year and was voted the best butter-croissant maker in Paris and the surrounding Île-de-France region by the Paris-based association of professional bakers, said he baked only straight croissants because they were easier to roll and fit neatly in a baking tray.

“I can understand the importance of symbolism and tradition, but straight croissants are more practical to make,” Mr. Turquier said by telephone from Paris.

While the croissant is associated with France, the pastry originated in what is now Austria, as a crescent-shaped roll called a kipferl.

Origin myths abound; one account is that Viennese bakers, drawing on an Ottoman emblem, came up with the crescent-shaped roll to celebrate the defeat of Turkish forces that ended their siege of Vienna in 1683. But some food historians say the kipferl appeared in Vienna as early as the 13th century.

According to Heather Arndt Anderson’s “Breakfast: A History,” the croissant was introduced to France in the late 1830s, when an Austrian artillery officer named August Zang founded a bakery, Boulangerie Viennoise, that sold kipferl. The rolls caught on, and the croissant was born, along with a name befitting its distinctive shape.

Some observers took to Twitter to express their disbelief that British jam-spreaders were unable to navigate a traditional croissant’s curved edges. “Utterly preposterous. Croissants are curved traditionally. Must be another EU directive!” wrote Timothy William of Belfast, Northern Ireland. Others mocked what they saw as a marketing tactic by the retail chain.