This means many of London’s fast-paced restaurants sometimes serve food prepared with small amounts of, for example, animal stock in veggie meals or of wheat in dishes labelled as gluten-free.
However, this is not deliberate but happens accidentally because of the speed employees have to work in busy and often understaffed kitchens.
Some 14% of chefs admitted that diners at their restaurant have to ask the waiter to check which dishes suit their needs because this is not otherwise labelled on the menu.
Hospitality recruiter, The Change Group, undertook the survey of 102 chefs working in fine-dining venues in London.
Gluten was the number one intolerance restaurants take into consideration, mentioned by almost nine out of 10 chefs (87%).
Other food intolerances and allergies accommodated included dairy (50%) and egg (43%) ingredients. Just 47% of chefs said their venue catered to people with a nut allergy.
Almost 50% of chefs said they had received on-the-job training in diet and nutrition, and just over one third of chefs (37%) said they had learned about these topics as part of a formal chef training course or through attending a separate course, specifically on diet and nutrition (15%). Some 5% of chefs claimed to have no formal training on nutrition or diet at all.
Almost half (48%) of chefs working in fine-dining venues said their restaurant offers vegetarian options and 42% offer vegan dishes.
One third of chefs said their restaurant took part in Veganuary, a campaign that encourages people to try vegan food during January.
While 42% of restaurants use menu icons and 21% use separate menus to indicate suitable dishes, 44% of chefs indicated that the responsibility to ask about food allergies and explaining which dishes will be appropriate to diners falls to front-of-house staff.
Almost three quarters (69%) think restaurants should provide diners with more nutritional information such as calorie count, sugar and salt content.
Some 60% of chefs also think restaurants should be offering alternatives to people with particular preferences, such as for ‘paleo’ diets, as well as 61% thought this for food intolerances.
In order to support more healthy eating, chefs are also cutting down on a number of ingredients sometimes associated with less, healthy diets including gluten (36%), salt (34%), fat (33%), sugar (30%), dairy (26%) and meat (15%).
The Change Group co-founder and director Craig Allen said: “Diet and nutrition are now key to what diners expect from fine dining and gastro establishments, and our data shows that restaurants are responding really well to this demand."
He added: “Many restaurants are focusing attention on diet and nutrition and there is a very high level of training, on the job and externally, on diet and nutrition.
“The reality of today’s busy, often understaffed kitchens is that a significant minority of chefs are reporting they work in restaurants that can allow contaminants in dishes that are meant to be vegan or gluten-free.
“Equally, front of house, many diners may still need to check with the waiter that a dish is suitable to their needs as this may not be marked on the menu.
“This is further evidence of the pressure restaurants face to deliver against customer expectations when so often they are struggling to get experienced help.
“We would advise diners with allergies and severe intolerances to check whether there may be small amounts of restricted ingredients in their dish to ensure they choose something suitable.”
Meanwhile, a significant number of young people aged between 16 and 24, and suffering from food allergies or intolerances fear eating out in pubs and restaurants, new research claimed.
Released by the Food Standards Agency (FSA) in partnership with Allergy UK and the Anaphylaxis Campaign, the study claimed that six in 10 young people with an allergy or intolerance avoided eating out in the past six months.
This rose to 64% of food allergy sufferers avoiding eating out and dipped to 53% of those with a food intolerance.