(CNN) -- Celebrity chef Jamie Oliver's restaurant empire in the United Kingdom has collapsed.
The entrepreneur and anti-junk food campaigner said Tuesday that the restaurant business was being placed into administration, or bankruptcy protection.
The group includes Jamie's Italian chain, Jamie Oliver's Diner at Gatwick Airport as well as steakhouse Barbecoa and Fifteen London, a restaurant Oliver started in 2002 to train young unemployed people.
KPMG, which has been appointed administrator, said in a statement that 22 of the group's 25 restaurants have closed, with the loss of about 1,000 jobs.
"Both Jamie's Italian restaurants and Jamie Oliver's Diner at Gatwick Airport will continue to trade in the short term while the joint administrators explore options for the site," KPMG added.
Oliver's international restaurants, including branches of Jamie's Italian, as well as Jamie's Pizzeria and Jamie's Deli, will continue to run as normal.
"I am deeply saddened by this outcome and would like to thank all of the staff and our suppliers who have put their hearts and souls into this business for over a decade," he said in a statement.
Oliver launched Jamie's Italian in 2008 with a focus on casual, mid-market dining with quality ingredients.
But the industry has become increasingly crowded in recent years. Casual chains are everywhere. Even fast food restaurants now offer fresh ingredients. That's piled the pressure on incumbent players.
Oliver pumped millions of pounds into the business in recent years but eventually had to admit defeat in the face of what he described last summer in an interview with the Financial Times as a "perfect storm" of rising rents, wages, food costs, as well as the impact of Brexit and changing shopping habits.
"The current trading environment for companies across the casual dining sector is as tough as I've ever seen," KPMG partner Will Wright said on Tuesday, adding that it had proved impossible to stabilize the business or find new investors against the backdrop of rising costs and "brittle consumer confidence."
Oliver is best known as a television star, book author and activist. His show "Naked Chef," which first aired on the BBC, eventually made him a household name.
More recently, Oliver has focused on campaigns for schools to serve healthier lunches in both the United Kingdom and the United States.
His restaurants have been a mixed bag. Oliver's Union Jacks pizza restaurants also floundered, and the last one reportedly closed in 2017.