Vegetarians can no longer enjoy some of the UK's most popular chocolate bars following a recipe change by Masterfoods.

Mars, Bounty, Snickers, Twix and Milky Way, as well as Maltesers and Minstrels, are now off the list of foods veggies can eat because they now include whey containing animal rennet.

"Due to a change in the ingredients used in our chocolate recipes from 1 May 2007, many of our products now contain whey," said Masterfoods in a letter to a consumer and seen by The Grocer.

"This is a by-product of the cheesemaking process and uses rennet from an animal source."

Vegetarians reacted angrily to the move. "For some incomprehensible reason they are using animal products, when all of these items have previously been produced using vegetarian alternatives," said a Vegetarian Society spokesman.

"There are about three million vegetarians in the UK, which is a significant part of the UK market. It is very disappointing that Masterfoods products are no longer vegetarian-friendly. We hope the company will reconsider this move."

Paul Goalby, Masterfoods corporate affairs manager, said: "Since changing the sourcing of our ingredients we are no longer able to ensure our chocolate will be animal rennet-free, and so we made the principled decision to admit it was not guaranteed to be vegetarian. If the customer is an extremely strict vegetarian, then we are sorry the products are no longer suitable, but a less strict vegetarian should be fine to enjoy our chocolate."

Products with a best-before date up to 1 October are still suitable for vegetarians. The company is offering a refund to those who cannot eat animal rennet on any bar that has a later best-before date.

n Masterfoods is poised to revert to its original company name Mars, as part of a global move to bring all the company's businesses under one banner.