The Mars bar: fuel for thousands of ascents of hills from the majestic Ben Nevis to the humbler slopes of the Cotswolds.

And fuel for a row which involved an international company, MPs and the massed ranks of the Vegetarian Society. In a salutary lesson in the power of consumerism, the makers of the gloopy aid to work, rest and play have been forced into an embarrassing climbdown and abject apology.

The row embroiled Masterfoods, the company that makes Mars as well as other sugary chocolate confectionery, when it announced it would change the type of whey used in its products. Henceforth, it would make Mars bars using rennet, a by-product of veal which comes from the calves’ fourth stomachs – mmm, nice!

The Vegetarian Society (VS) leapt into action at the news, understandably upset that its members would have to make the choice between chewing a product containing traces of calves’ enzymes and eschewing their favourite choccie for another brand.

More than 6,000 complaints flooded into Mars’s headquarters; an Early Day Motion – a type of parliamentary petition – garnered support from 40 MPs and local newspaper editors were bombarded with letters in the run-up to this week’s National Vegetarian Week.

A VS statement said: “The Vegetarian Society is extremely disappointed to learn that favourites such as Mars, Milky Way, Bounty, Snickers, Galaxy, Twix and Maltesers are now all unsuitable for vegetarians.

“At a time when more and more consumers are concerned about the provenance of their food, Masterfoods’s decision to use non-vegetarian whey is a backward step. Mars products are very popular with young people and many will be shocked to discover that their manufacture now relies on the extraction of rennet from the stomach lining of young calves.”

Faced with a growing boycott of their products, Masterfoods’s UK managing director Fiona Dawson made the U-turn. She said: “We made a mistake. We apologise.

“The consumer is our boss. Therefore we listen to you and your feedback. We have received lots of feedback that this decision has made it difficult for some of you, especially those of you who are vegetarians, to continue to enjoy our products.

“As a company we value openness, honesty and diversity and we believe that anybody should be able to choose freely from our range of chocolate brands.

“But being sorry isn’t enough. Therefore we commit to you today, that we at Mars UK will ensure that a selection of your favourite brands – Mars bars, Snickers bars, Galaxy and Maltesers, will be suitable for vegetarians in the near future. To this effect we are starting to change our manufacturing process today.”

So all you vegetarian lovers of the outdoors will soon be able to pack your rucksacks with Mars bars once more. Veggies 1, International Capitalism nil.

A further statement from Mars said: “Currently we cannot guarantee that our products contain vegetarian rennet.

“However, we are starting to change our manufacturing process with immediate effect. We want to get our vegetarian products on the shelves as soon as possible. During this process of changing the recipes we will provide updates on this consumer care website, on a regular basis. If you are not sure about the suitability of our products please call us on 0845 0450042.”

Mars said that the following products will again suitable for vegetarians: Mars, Snickers, Galaxy, Maltesers, Minstrels, Revels, and Ripple. However, Twix, Bounty and Celebrations are not vegetarian-friendly.