Food industry giants including Tesco and Danone have joined charities to call on Andy Burnham to make food security a national priority alongside energy and defence.
The letter, also signed by Sainsbury's, Aldi, Waitrose and Co-op, charities including Barnardo's, Amnesty International UK and WWF-UK, health campaigners, investment companies and farming organisations, warns that the next "food shock" is "not a question of if, but when".
It says: "Each new shock lands on a food system with less capacity to absorb it. British production of fruit and vegetables has fallen 16% since 2015, and we now import 78% of our supply.
"The next food shock is not a question of if, but when.
"To meet it prepared, food has to stop being an afterthought for the Government: we need mechanisms to put food high on the priority list of every part of government, both national and local, so that any decisions that impact on health, farming, planning, and trade secure better access to healthy and sustainable food for everyone.
"The cost of doing nothing on this issue is already falling on those with the least resource, with food insecurity already affecting 15% of households with children.
"Economic pressures continue to push a healthy diet further out of reach for many, with the NHS then left to pick up the bill."
It calls on Burnham to urgently introduce a Good Food Bill to act as a legally binding framework to improve national food and nutrition security, public health and food system resilience.
International conflict has pushed fertiliser costs up by around 40% since last year, while more frequent extreme weather events, highlighted by this summer's wildfires across Europe – are making harvests vulnerable.
Earlier this year, the Government's own National Security Assessment concluded that global biodiversity loss poses a direct threat to the UK's food supply.
UK food prices are on track to be 50% higher by November compared to levels at the start of the cost-of-living crisis in mid-2021, according to the Energy and Climate Intelligence Unit (ECIU) think tank said