Carter joined Blakemore from Asda in October 2008 as Blakemore's first-ever marketing director.
He masterminded its Pounds Down round-pound strategy, which was adopted by three-quarters of the Spar stores serviced by AF Blakemore and boosted sales of the products on promotion by 30%.
Carter also helped Blakemore introduce the first Eurospar stores Spar's small supermarket format to the British mainland and the new 1,000 sq ft store format last month.
"Ged and the new marketing team worked together to improve our promotional offer, grow greater own-label participation and a sustainable pricing strategy," said Dennis Evans, MD at Blakemore Distribution.
Carter had also helped boost sales at Spar stores by improving in-store marketing and launching promotions on categories such as fresh meat and breakfast goods, he added.
Boots refused to comment on Carter's role as head of instore marketing, but industry insiders speculated he had been hired to help boost its grocery range, which was being expanded as part of a tie-up with Waitrose. Carter has spent all of his career in grocery, having worked at The Co-op Group for 20 years before joining Asda.