Sainsbury's has been caught prominently advertising '100% British cauliflowers' in stores despite also selling cauliflower from countries such as France and Spain, an investigation by The Grocer has revealed.

Sainsbury's was found to be displaying a Union Jack-emblazoned '100% British cauliflowers' sign in a number of stores this week.

On Monday, in Sainsbury's New England Street store in Brighton, pre-packed wholehead ­cauliflowers with a French country of origin label were being sold directly underneath the sign.

Sainsbury's claimed it was an isolated incident when The Grocer approached it for comment. "This is a simple mistake as this PoS should have been removed and we are contacting the store to ask them to change it. It was not a deliberate attempt to mislead our customers," a spokesman said.

However, on Tuesday, in the retailer's Horsham store, pre-packed Spanish cauliflowers were being sold beneath the same signage. On the same day, in Sainsbury's Streatham Common store in London, mixed cauliflower & broccoli floret packs containing French cauliflower were on sale close to the sign.

Research by Field Agent, which carries out field research in stores, also revealed that French wholehead cauliflowers were being sold in Sainsbury's Wrexham store, and mixed broccoli & cauliflower florets including French cauliflower were being sold in Sainsbury's Staines and Nottingham Castle Boulevard stores. All three stores were displaying the British signage.

Sainsbury's said that, ­although it endeavoured to source 100% British cauliflowers, poor growing conditions meant it currently had to source some product from elsewhere. It had taken immediate action to ensure consumers were not misled, it added. "We have contacted all stores asking them to review and check their signage to ensure it reflects the correct country of origin."

In its Horsham store, Sainsbury's was also displaying '100% British Lettuces' and '100% British New Potatoes' signs despite selling So Organic Lettuce from France, So Organic Little Gem Lettuce from Spain and Iceberg ­lettuce from Spain. Pre-packed baby new potatoes from Israel were also being sold. The Grocer was unable to confirm whether other stores were doing the same.