The Tories want details of food served in NHS hospitals published so the public can see if ingredients are locally sourced.
Shadow environment secretary Nick Herbert announced the move as part of plans to encourage the public sector to use more British food.
A new guide will set “clear, simple and workable” standards for NHS bodies and councils to implement in schools, hospitals, care homes and prisons.
All new contracts for Whitehall departments and government agencies will be required to only buy food that meets British standards of production, where this can be achieved without increasing overall costs.
The plans are part of the Conservative Party’s Honest Food campaign to boost locally sourced food and make country of origin labelling clearer on meat.
Mr Herbert said: “Under Labour, our self-sufficiency in food has fallen, government departments are sourcing less British food, and taxpayers have no idea how much of the food served in their local school or hospital is British.
“We need a government that backs British farmers, takes a lead in sourcing more local food and is transparent about what food the public sector is buying.”
Some £2bn a year is spent on food procurement by the public sector so spending the money more wisely would have a major impact, he said.
He said a code for sustainable food would provide clear standards against which public sector bodies could be judged and councils.
And he said NHS organisations and local councils should be required to publish their food procurement contracts so parents, patients and residents can see how much of their money was being spent on local food.