The private letters, dubbed the black spider memos, were published after a 10-year legal battle by the Guardian, and show how the Prince of Wales wrote to several government departments and the Prime Minister between 2004 and 2005.
In part of the letter to Blair written in February 2005, Charles wrote that the "dominant position of the retailers is the single biggest issue affecting British farmers and the food chain".
Blair replied in March noting his concerns about "retailers 'arm lock' on suppliers" but said the government "can and will now more easily run with a voluntary code".
Charles also wrote to former trade and industry secretary Patricia Hewitt, health secretary John Reid and former culture secretary Tessa Jowell among others in 27 letters.
He also discussed matters such as badger culling, the armed forces and other agricultural issues.