The contract already includes a quarterly interview with customers in Somerfield's 1,000 stores and will now have a bi-annual mystery shopper element for the first time.
For some of the chain's smaller outlets, this activity is expected to be carried out more regularly, according to Nunwood, which has held the account for the last five years.
The mystery shopper exercise is set to take into account each store's facilities, such as its location, parking and size, to ensure the results are comparable across the chain.
Jennie Murray-Smith, Somerfield consumer insight manager, said: "Nunwood is a trusted partner in our business and delivers excellent insight that helps us understand our customer better and meet their needs."
Pic: Somerfield
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .