Mr Norman will continue to work full time until December but will then move to a part time role. It is not yet clear how much time Mr Norman will devote to Asda but the company said it was unlikely to be less than two days a week. "We'll take stock in the new year but at no stage will he do less than two days," Mr Leighton said.
Mr Norman's move has come earlier than expected and it immediately ignited speculation that he might be preparing to leave Asda altogether, possibly to pursue a career in politics. Mr Norman's political ambitions are well known and he has been mentioned as a possible Conservative candidate for Harrogate, near his Yorkshire home. Asda was quick to dismiss fears that the group's talismanic leader was set to leave. "Archie's first priority is to Asda," the company said.
Allan Leighton said he was delighted to be taking over and said the reshuffle demonstrated Mr Norman's continuing commitment to the group. "It means we are both committed to the business for a period of time."
Asda shares fell 4p to 115.5p on the news though half the fall was due to the shares going ex-dividend. City analysts were divided on implications of the changes. One said: "Asda's recovery over the last few years is firmly down to Norman's management and any suggestion that he will be less involved will not be taken well by the City."
Others expressed surprise at the timing of the announcement but said Mr Leighton was a good choice. "We've got a great deal of respect for him and he has been Archie's right hand man for some time. It has come a bit earlier than expected but I don't think Archie well be leaving for at least two to three years."
Mr Leighton, 43, joined Asda as group marketing director in 1992 after 17 years with Mars Confectionery and two with Pedigree Petfoods. He was appointed deputy chief executive last year. He has worked closely with Mr Norman and has been groomed for the top job, increasingly taking the lead in presentations to the City.
He pledged to continue the strategy that has transformed Asda's fortunes: "Mr number one priority is eto keep going the way we are. There's lots to do. We still have a third of the stores to refurbish, for example."
Archie Norman, 42, joined Asda as chief executive at the nadir of the company's fortunes in December 1991. Heavily loss-making and saddled with a mountain of debt, the company was losing ground to more powerful rivals such as Sainsbury's and Tesco. The company gradually recovered by competing as a lower priced alternative to its rivals while Mr Norman fought a series of high profile campaigns for lower prices of books, medicines and even bananas.