Safeway aims to build five new areas into the site by next spring - a fish counter, a bakery, a home entertainments area, a fresh meat department, and a mock flower market.
The centre opened in March and currently houses a deli, Fresh to Go and Café Fresco facilities, a 60-seater auditorium, and an IT suite. The venue is also used for Safeway's "retailtainment" training, which involves teaching skills such as pizza tossing.
Safeway estimates that 5,000 staff will have passed through the site by 2003 and it hopes the increase in capacity will enable it to deal with 13,000 staff per year.
Safeway training manager John Batten said: "This is the only centre of its kind and we are immensely proud of it.
"None of the other food retailers have training centres, all their staff learn in a store environment."