With the help of his two sons, Marcello and Alessandro, the business has continued to defy the recession even in parts of the country where trading has been toughest.
Turnover across the group, which comprises six San Carlo sites in the north of England and Signor Sassi in London's Knightsbridge, has jumped to £22m in 2009 from £17m - and now the company is planning a major expansion of the Signor Sassi across the Middle East, having already opened two restaurants in the region.
Although Di Stefano has owned San Carlo since 1992, he only bought Signor Sassi in Knightsbridge in 2007, after dining there for more than 20 years. "I loved eating there but saw some things we could improve. Within two years we had doubled the turnover," he says.
In a strange twist of fate, the restaurant's next major step was sealed by a diner. Marzouk Al Kharafi is chairman of Middle East catering giant Americana, and was a regular in Signor Sassi whenever he was in London. Americana already operates international franchises for global brands including TGI Fridays, Krispy Kreme, Pizza Hut and Costa Coffee.
Al Kharafi struck a deal with the Di Stefano family to franchise the restaurant across the Middle East with plans for 22 branches in total. The latest of the two restaurants has been set up in 360 Mall in Kuwait City, joining brands like Yves Saint Laurent, Burberry and Dolce and Gabanna. But other branches are targeted for Dubai, Riyadh and Cairo.
"It was a proud moment for me when this man chose our restaurant," Carlo says. "There are many great Italian restaurants in London, like Cipriani and Locatelli, but he chose us because we were his favourite."
Eldest son Marcello is in charge of the Middle East expansion and is determined that the firm's commitment to quality will not be diluted. "We are learning the franchise model as we go but every restaurant will be true to the elements that have made Signor Sassi successful," he says.
"You have to lay down certain standards but also be flexible so chefs can adapt the menu and come up with their own dishes. Chefs are creative people and if you restrict them too much then you risk losing them," adds Marcello.
Staff play a vital role at San Carlo and Signor Sassi with 15 chefs in the kitchen in Knightsbridge and 27 in the biggest operation in Manchester. The firm works with two agencies in Italy to provide staff to keep everything as authentic as possible and will continue to do so with its Middle Eastern outlets.
"The heart of the business is the kitchen," says Carlo. "You cannot compromise over quality of people and ingredients. The same applies to front of house. Many of our people have been with us for years and help make the restaurants so special."
The firm is keen not to expand too quickly, despite its ambitious plans, and the owners would rather wait for the best sites than race ahead in the wrong premises.
Marcello says: "We waited four years to find the right venue in Liverpool. The right location is vital and one of the key mistakes people make is not taking their time and rushing in because they are so keen to get going."
The family wants to open another Signor Sassi in the St James' area of west London but will wait to find a suitable venue.
But in November, the latest venture opens in Manchester with San Carlo Cicchetti bringing Venetian-style tapas to the city. The 1,700 sq ft premises will occupy the ground floor of the House of Fraser store next to the existing San Carlo restaurant. It will offer traditional breakfast in the mornings, then the small plates known as cicchetti which are a speciality of Venice.
"Sharing lots of different dishes is a popular way of eating now and the new venture reflects that. People will be told the source of all the ingredients and we will offer 25 different wines by the glass," explains Alessandro.
San Carlo Cicchetti will employ up to 20 new staff and the family hopes the concept will prove popular enough to spread across the country.
Explaining why he feels the company has been successful so far, Carlo says: "We haven't put up our prices or tried to exploit our customers. We want people to come here and enjoy the food and wine and have a good time. We want staff here who love their job and that feeling spreads across the place. Some people say Italians were made to feed people and there's a lot of truth in that."
Having the family involved adds to the individual feel of the business and both sons share their father's passion for food.
Marcello says: "When the recession hit, people didn't stop going out to eat completely. They just got more discerning about where to spend money. A lot of restaurants have gone out of business but there are reasons for that and reasons why others prosper. People can see the difference between us and some of the chain operations who offer Italian food which is not such good quality."
"You look at some modern restaurants and it's like eating in a hospital," Carlo adds. "Everything is so over-designed and clinical while some of the fine-dining places are so formal you can't relax. That's not my idea of a good meal. I want our customers to enjoy themselves and tell everyone what a good time they had."
He's certainly good to his word. Lunch at Signor Sassi with Carlo is often interrupted by him sharing a joke and a hug with regular diners. He spends his time touring around the San Carlo sites and visiting Signor Sassi to make sure everything is running like clockwork. "Why would I want to do anything else? This is my life" he says.
The famous guest who sparked most debate among fellow diners was ex-deputy prime minister John Prescott.
Marcello Di Stefano explains: "It was really strange when he used to come into our Manchester restaurant. He had a certain image in the papers and a lot of people were asking me why we let him eat here. Usually people tend to ignore celebrities but Prescott provoked a real reaction. Of course we let him enjoy our food and he turned out to be a real great guy who charmed everyone."
Manchester United and City footballers are regular guests. Ronaldo ate two or three times a week when he was at United. But even he couldn't keep up with Sven-Goran Errikson's appearances when he was manager of City.
"He was in here almost every night to eat or get a take-away," Marcello says. "He and his assistant Tord Grip would pop in Sainsburys then here for take-home antipasti on Champions League nights. It was funny to think of them sitting on the sofa watching the matches together."
SAN CARLO GROUP
Annual Turnover £22m
Number of Employees 400
Number of Restaurants Seven - Birmingham, Bristol, Manchester, Leicester, Liverpool, Leeds and London (Signor Sassi)
Average Spend £35-£40 San Carlo, £55 Signor Sassi
Food v drink revenue split 65% food to 35% drink
Covers per week 5,000 in biggest branch - San Carlo Manchester