Hospitals could run out of much of the imported food that goes into millions of patient meals in the event of a no-deal Brexit, the Department of Health and Social Care has admitted in a letter to all NHS trusts in England.

The department said it was urgently planning to cope with potential “short supply of certain ingredients imported from the EU”, which involves advising suppliers how to use “substitute foodstuffs to maintain nutritional balance” of meals.

The letter – part of the government’s cross-departmental planning for a no-deal Brexit – shows the concern about practical difficulties for key public services from border delays and increased trade friction in the event of no deal.

The Observer understands planning is also under way to prepare organisations that provide meals to schools, prisons and care homes.

The letter, details of which have been provided to MPs on the health and social care select committee by the deputy chief executive of NHS providers, Saffron Cordery, tells trusts: “Instructions will be given to major producers of patient meals to put in place contingency arrangements, to account for short supply of certain ingredients.”

It adds that “guidance will be provided to hospital caterers, procurers of patient food and catering services, and PFI providers on actions to take in preparing to use substitute foodstuffs to maintain nutritional balance of patient menu/meal offerings.”

Andy Jones, chairman of Public Sector 100, which represents catering associations working in the public sector, who has seen the letter, said he was “very, very concerned” that supplies would be affected. While he believed trusts could make plans that would be effective for weeks, after that, problems would mount and the position would become critical. He said the fact the department had sent the letter to trusts suggested ministers now believed a no-deal was ever more likely. He said about 40% of food provided to in-patients was imported from the EU, much of it under the “just-in-time” system, which ensures speedy delivery. Much of the chicken, and salad consumed out of season, came from the EU.

“It is not just of case of whether we will be able to get enough, if there is no deal,” he said, “but also whether we will be able to afford it. Good food is vital for patients. Food is like medicine. If patients don’t get it then in some cases they will not get home. One thing we will see I think is choice disappearing. People will just be given what we can get our hands on.”

The Tory chairman of the all-party health select committee, Sarah Wollaston, said: “It is becoming ever clearer that we are not just facing a shortage of drugs but also many other things which hospitals need to function. Food is one them. The cost and work involved in dealing is staggering. Surely there is a better use and of time and money.”

Shadow Health Secretary Jonathan Ashworth said: “Not only is the health secretary buying up fridges to stockpiling vital medicines but it now seems hospitals might not even be able to feed patients on their wards. No one put that on the side of a bus advertising the benefits of Brexit. The health secretary urgently must outline his plan to support hospitals through this chaotic Brexit so patient care doesn’t suffer.’

A Department of Health and Social Care spokesperson said: “The government is confident of reaching a deal with the EU that benefits patients and the NHS. However, as a responsible government we are also preparing for a range of potential outcomes in the unlikely event of a no deal.

“As part of our contingency planning, we are taking all necessary steps with NHS England, suppliers and pharmaceutical companies to ensure patients continue to receive the high standards of care they expect.”