Jools Oliver, wife of the celebrity chef Jamie Oliver, set social media abuzz in December when she posted pictures of the couple’s £9m home. The seven-bedroom, Grade II-listed property in London’s rarefied Hampstead was as sumptuous as might be expected for a chef who has built a £150m fortune from a business spanning books, TV, endorsements and restaurants.

But as Jools’s followers admired the fruits of Oliver’s success, he was battling to save Jamie’s Italian, the centrepiece of his restaurant division. In December, Oliver pumped £3m of his own money into the business, and in January the chain said it would close 12 of its 37 UK branches, as part of a rescue deal with its creditors to keep trading.

Last week, court documents emerged showing Jamie’s Italian had debts of £71.5m. This comprised £30.2m of overdrafts and loans, and £41.3m owed to HMRC, landlords, suppliers and other creditors. Staff were owed £2.2m.

Oliver’s spokeswoman says the £71.5m figure paints a distorted picture – £47m is covered by loans from HSBC and Jamie Oliver companies. She adds that money owed to suppliers, the taxman and employees is standard for a business and, she says, everyone has been paid. But the documents show the business was on the verge of going bust.

When Jamie’s Italian opened its first branch in 2008 in Oxford, customers lined up outside to sample its menu of rustic Italian staples with a “Jamie-style twist”. The Guardian praised it for good food, fair prices and large portions. For a while the public seemed to agree as the business expanded rapidly, peaking at more than 40 branches.

So where did it all go wrong? Warning signals emerged in early 2017, when Jamie’s Italian blamed intense competition and rising costs, partly as a result of Brexit, for the closure of six branches. When accounts for 2016 were published in October, the business had slumped to a £9.9m pre-tax loss from a profit of £2.4m a year earlier. The loss was caused mainly by the costs of branch closures and handing back a lease for a site in King’s Cross where Oliver had scrapped plans for a giant restaurant, pub and head office complex.

The accounts said the chain’s remaining branches were outperforming the market and that the brand “remains incredibly strong”. A cut-price lunch offer had brought in more customers and the business was set to increase earnings “long into the future”.

But the restaurant business’s chief executive, Simon Blagden, left in October along with the finance director, Tara O’Neill. Jon Knight, who ran the international arm of Jamie’s Italian, took over the UK operation and the business was brought under the wing of Paul Hunt, the husband of Oliver’s sister Anna-Marie.

Hunt, a former City trader who was fined £60,000 in 1999 for insider trading, had overhauled Oliver’s media and licensing operations after taking charge in 2014. Oliver is now said to be more involved with the restaurant business, having left it to others in recent years.

To some extent, the troubles at Jamie’s Italian reflect the wider market for casual dining. Business boomed as the economy picked up after the financial crisis and consumers spent more on eating out. But a glut of new openings led to intense competition, combined with rent rises, higher business rates and increasing food prices. Byron, the burger chain, had to be rescued in January after expanding too quickly.

Peter Martin, vice-president at the food and drink consultancy CGA, says savvy operators such as Nando’s and JD Wetherspoon have remained successful by adapting to changing tastes. The court documents for Jamie’s Italian paint a picture of under-investment, complex menus and ill-judged branch openings.

“With this much choice in the market, customers will take it unless you stay fresh and relevant,” Martin says. “When Jamie came on to the scene it was new and exciting. There were queues outside the Oxford branch and they were taking samples out for people to try. But the market has become more exciting generally and you have got more people doing that sort of thing.”

The crisis at Jamie’s Italian has followed a series of business setbacks for Oliver, who by his own admission has “fucked up” 40% of his ventures and lost £90m of his wealth since 2014.

In 2015, Oliver shut the last branch of Recipease, his chain of cookery shops. In 2017, he closed the last of his four British-themed Union Jacks restaurants. And in October his food magazine, Jamie, stopped publishing after almost 10 years.

There may be further trouble ahead. Oliver has put both branches of Barbecoa, his upmarket barbecue chain, up for sale. Barbecoa did not even have a honeymoon period. When the first restaurant opened near St Paul’s Cathedral in London in 2011, the Observer’s Jay Rayner said it would be laughed out of town in New York.

Yet away from his restaurants, Oliver’s business continues to make plenty of money. At Jamie Oliver Licensing, which covers his endorsements and range of products and tie-ups, pre-tax profit rose to £7.3m from £7m in 2016. Profit at Jamie Oliver Holdings, which covers his media interests, rose to £5.4m from £1m. Oliver paid himself £10m in dividends for the year – £6m from licensing and £4m from media. He has never taken any money from the restaurant business.

It may be no surprise that Jamie the brand is thriving as Oliver the restaurateur struggles. His path to fame, fortune and influence started when TV producers filming at the River Cafe in London spotted the chatty junior chef and offered him his own show. The Naked Chef, broadcast in 1999, made Oliver a star. Recipe books, endorsements and campaigns for healthier eating followed, making him rich and famous before he opened a single restaurant.

Paolo Aversa, associate professor of strategy at Cass Business School in London, says Oliver’s business is essentially a brand built around his personality with a restaurant operation running alongside. This is not necessarily a bad thing, he says, because many companies maintain unprofitable activities that enhance their image – but if things go wrong the main brand can be damaged.

“You can argue that a company that sells an idea of better eating habits, healthy food and so on should have some kind of flagship business that reminds the customer where this all comes from,” Aversa says. “I think Jamie’s Italian reinforced the image and it still does to a certain extent. People still see the restaurants around. The question is: is it worth the financial underperformance?”