Oliver has already spent four years with Sainsbury's

The 29-year-old will appear in a new television and radio advertising campaign for the company.

Oliver, famed for his chirpy Naked Chef persona, will act as a "quality detective" in the adverts, visiting suppliers and buyers.

He will also work behind-the-scenes on developing new products for the supermarket, Sainsbury's said.

Oliver has worked with Sainsbury's for the past four years, appearing in more than 65 advertisements and helping develop products.

'�200m profits'

The supermarket has not revealed how much Oliver's new contract is worth, but a report out in 2002 revealed the campaigns he featured generated �200m in profits over two years.

When Oliver recommended spreading truffle butter under the skin of Christmas turkeys, more than 50,000 jars of the products were sold.

Oliver said: "Working with Sainsbury's gives me the chance to reach and inspire millions of customers with fresh new ideas."

Dominic Rowell, national advertising manager at Sainsbury's, said: "Jamie is enormously popular with our customers.

"Whether it's through adverts or product ranges, his passion for food and energy have managed to grab and maintain consumer attention."