From now until 6 July, the packaging of Co-op own-label tomatoes, mixed peppers and iceberg lettuce will display an online promotional code. If customers type the code into the Co-op Group's food website, they will be entered into a prize draw to win one of three Union Jack Minis or one of 100 iPod Nanos.
The society said the competition was to show its support for British growers by sourcing as much of its salad range as possible from the UK.
The range, which includes tomatoes, peppers, lettuce, cucumbers, celery, radish, cress, spring onions, beetroot and growing herbs, had been produced as feedback had showed customers wanted to buy salad that was fresh, seasonal and grown in Britain.
Meanwhile, the Co-op Group has become the latest retailer to launch an app. The Co-operative Food's Grown by Us app allows shoppers to scan barcodes of Grown by Us lines in stores to view aerial photos of farms where the products were grown.
It also provides information about each farm, the produce grown there, and information about the farm managers. The app will also have a store locator in the near future.
"This is a great way for our customers to really connect with our farms," said Peter Jones, a senior marketing manager at the Co-op who developed the app.