A cost-cutting exercise saw bestsellers like Mars bars, Snickers, Twix and Maltesers replace their vegetable source with one containing rennet, a natural enzyme produced in the stomachs of calves.

The move provoked outrage among customers and forced Mars to revert back to its original recipes. "We underestimated the impact this would have," said Fiona Dawson, MD of the Mars snack business in the UK. "We had made a mistake, for which I am sorry."