The grocery industry watchdog is to make a rare intervention in a Yorkshire sprout grower’s £3.7m legal case against Aldi over the discount chain’s decision to terminate a long-term supply deal.

In papers filed at the high court, W Clappison Ltd, which produced sprouts for Aldi’s UK arm for 13 years, said its supply agreement was ended in February last year at planting time without reasonable notice so it was unable to find new clients immediately. It said it was forced to cease sprout production and sell off its machinery.

The farmer, who claims to have been Yorkshire’s last commercial sprout grower, says in the papers his business had bought land and equipment based on assurances of ongoing demand from Aldi, which represented almost 40% of its sales, with other customers including Morrisons and Iceland.

The lawsuit alleges Aldi’s behaviour was in breach of the groceries supply code of practice (GSCOP), a set of rules for dealing with suppliers by which large retailers must abide.

The rules are overseen by the Groceries Code Adjudicator (GCA) – currently Mark White – who can carry out investigations and issue fines of up to 1% of UK sales if he finds wrongdoing.

A spokesperson for White said: “The GCA has applied to intervene in the proceedings to assist the court in resolving the groceries code matters in dispute between the parties.” The intervention was first reported by trade news site the Grocer.

In 2022, White said he had “intensified” talks with supermarkets, partly because of concerns about products being delisted without reasonable notice. However, in the GCA’s survey of suppliers this year, 14% said this remained a key issue, the same proportion as the prior year.

Aldi wrote to Clappison several weeks after ending the supply contract by phone saying this was due to the grower’s terms “being uncommercial and Aldi looking to consolidate business”.

The supermarket said it gave six months’ notice and it had consulted and agreed a timetable for its annual tendering process and found its scheme appropriate.

An Aldi spokesperson added: “We are disappointed by the claims made by W Clappison Ltd as we go to great lengths to follow the relevant codes of best practice for managing supplier relationships.

“This is why we have consistently been ranked as one of the top supermarkets for conducting relationships fairly, in good faith and without duress in the GSCOP annual survey.”