This paper examines a particular accounting practice prevalent in the UK agriculture industry and reveals the ‘canopy of legitimations’ that appears to protect the practice and make it highly resistant to change. Agricultural gross margin accounting was innovated through Government sponsored agricultural extension programmes in the post-war period in Britain. The practice is not maintained primarily by farmers but rather by actors within Government agencies and agricultural service industries (including management consultants). New Institutionalism in Sociology (NIS) is used as a theoretical framework, and extended to consider the concept of legitimation as a reflexive process. Although the context is specifically UK agriculture, the theme of the protection of accounting methods by Government and other advisors is of more universal interest. The paper adds to the very few studies in the accounting literature that consider the agriculture and food industries.