A good way to support local farming businesses would be to encourage the public sector to buy British, campaigners have told the prime minister.
Love British Food, a group promoting local food, says 85% of the current public sector budget for food procurement should be spent with local businesses and farmers.
The public sector, which includes schools and hospitals, currently purchases £2.6 billion of food every year.
But campaigners say that while many public institutions do a 'huge amount' to support local businesses, they believe more can be done.
A letter has been sent to Boris Johnson explaining that British farmers and growers produce to 'some of the highest qualities in the world'.
It goes on to say that food producers have continued their work in 'the most challenging circumstances this year', and they 'deserve our support'.
Many signatories of the letter are people directly involved in public sector catering and procurement.
Prominent figures have also signed Love British Food's letter, including chef Raymond Blanc OBE.
The letter says: "Many of us from within the industry are hopeful that government is capable of doing more to help support local producers during this difficult economic period.
"We want to set one simple, but ambitious target: A firm objective to spend 85% of the current public sector budget for procuring food and catering services with local British businesses and producers.
"Progress has been made and we need to build on that success. We understand that there are challenges ahead, but where there is a will, there is a way."
Campaigners say public procurement tenders must encourage suppliers to participate, and institutions should support them through the tender process with an emphasis on encouraging small firms to apply.
"We need education, action and sufficient central support to make this possible," the letter adds.