It is a calorie-busting culinary concoction that has become as synonymous with Scottish food as haggis across the globe. The “Stonehaven deep-fried Mars bar” shot to international infamy after a young schoolboy first asked to have his favourite chocolate bar smothered in batter and plunged into the frier of an Aberdeenshire fish and chip shop.

But as the unlikely delicacy celebrates its 20th anniversary, the Carron Fish Bar – birthplace of the fatty treat – has suddenly incurred the wrath of the giant chocolate company that manufactures its main ingredient.

Lorraine Watson, who runs the Stonehaven fish and chip shop with her husband Charlie, has received a letter from one of Mars Chocolate’s lawyers, requesting that the chip shop should carry a disclaimer on any menus, and pointing out that the use of the bar for deep fat frying is “not authorised or endorsed by Mars Incorporated”. The chocolate company claims in its letter that deep frying the Mars bar, which recently had its saturated fat level cut, is “not in line” with the company’s marketing code aimed at promoting a “healthy active lifestyle”.

A shocked Mrs Watson – whose shop proclaims it is the “birthplace of the world famous deep-fried Mars bar” – explained yesterday how she had come to receive the letter from Mars.

Newspapers had reported that she was toying with the idea of applying for secured status for their famous invention under the European Union’s Protected Food Name Scheme, in line with other specialities such as the Arbroath Smokie, Parma ham, Cornish pasties and Champagne.

She said: “When I looked in to applying for special status and looked at all the paperwork I realised it would never be a viable thing for us to do. It would involve a lot of communication with Mars themselves and that just wasn’t going to happen. I was amazed when I got the lawyer’s letter because I really feel they are giving me a slap on the wrist when I haven’t tried to offend them.”

She added: “We have been selling this deep fried Mars product for 20 years and this is the first time we have heard from Mars. Have I really offended them that much? I think it’s sad that it’s come to this. But we are quite happy to put a disclaimer on the main menu for the shop because I don’t want any reason for them to come back and try some sort of court action against me.”

Ms Watson continued: “I didn’t know they had reduced the saturated fat content. But, of course, the deep-fried Mars bar isn’t healthy. We have never said it was. And I am quite happy to put a disclaimer up because my intention was not to offend the Mars bar product. I am proud of the product – it does my business very well and it must be doing their business very well.”

She said that the chip shop, which first encased the chocolate bar in batter in 1992, is still selling between 100 and 150 deep fried Mars bars every week – 70 per cent to visitors to the town. She said: “We get visitors from all over the world, from as far afield as Japan and America, coming to the shop and ordering our bar. I saw an Italian book on Scotland the other day and we were right next to Dunnottar Castle.”

A Mars spokeswoman said: “We are really flattered that customers of Carron Fish Bar like our product so much that it has now become a flagship product for the store. No application for a protected geographical indication has been filed to date. Should an application be filed, unfortunately, we wouldn’t be able to support it as deep-frying one of our products would go against our commitment to promoting healthy, active lifestyles.”

Evie Kyriakides, Mars’s senior regional trademark counsel for Europe, states in her letter to Mrs Watson: “We are flattered that you obviously like our Mars product so much and consider it a flagship for your Carron Fish Bar. However, we are concerned that the use and reference to our Mars brand and products may mislead the public into thinking that your products are in some way associated with, or endorsed by Mars, when this is not in fact the case. We are also concerned that your products are not in line with our marketing code, through which we promote a healthy active lifestyle to consumers and treats in moderation. As you may know, we have recently reduced the saturated fat level in our Mars bar recipe. Deep frying our Mars bar product, of course, counters this significantly. To avoid any consumer confusion in this respect, we would be grateful if you would insert a small disclaimer at the bottom of any menus you may have and a sign on display at your shop stating as follows: ‘Mars is a registered trade mark of Mars Incorporated. Our use of Mars is not authorised or endorsed by Mars Incorporated’.”

“As you will appreciate, Mars reserves all its rights in the event we become aware of increasing instances of confusion or dilution. I look forward to hearing from you as soon as possible. In the meantime I hope that the Carron Fish Bar continues to be a success.”