Teachers in schools in Kent have been told they may have to suspend classes and “adopt a carer role” in the event of disruption caused by a no-deal Brexit.

The warning comes as the government confirms it has activated a team in a nuclear-proof bunker under the Ministry of Defence to provide army support in a no-deal scenario.

No-deal planning will move from the Cabinet Office to daily meetings of the government’s emergency committee Cobra from next week. Also the military’s Operation Redfold will have authority to direct some 3,500 military personnel to move food and fuel and help with traffic congestion in Kent.

Schools in the county have been advised by local authorities to check on food supplies and warned that public transport and school coaches could be affected if there is “panic buying” of fuel, according to a document seen by the Guardian.

The schools have been warned they may have to consider looking after “stranded” children if parents are caught in gridlock.

Kent is expected to bear the brunt of any problems resulting from a no-deal Brexit because of potential delays caused by increased checks at Dover and Calais, which are used by 11,000 lorries a day.

In the seven-page advisory note, Kent county council also suggests teachers should plan what to do if air quality deteriorates. They are advised to reduce risk by ensuring children stay indoors with all “windows, doors and trickle vents” closed. The main concerns are the impact of congestion on staff, food and fuel.

Last year, the council warned it might have to deal with 10,000 lorries parked or queuing on its roads, with a knock-on impact on schools, hospitals, rubbish collections and morgues.

“During periods of staff shortage due to an emergency, before headteachers decide to close, they should consider two alternative courses of action,” it says. “First, consider suspending normal teaching and instead adopt a ‘carer’ role with classes being supervised.”

The second suggestion is to merge separate year groups if teachers in one of them are short.

The council points out this is preferable to closing a school, advising headteachers that in the event of a no-deal Brexit, they will have to consider the impact of forcing parents to leave work. If a primary school closes, “it might potentially result in several hundred working parents having to leave their place of work to look after their child”, it says.

The document adds: “These parents may be in an occupation that provides a vital service to the community, (eg nurses, carers, bus and lorry drivers, social workers or even teachers).”

If transport is delayed or cancelled and pupils are left waiting in schools, teachers are advised they may have to abandon their own after-school plans and “remain on site to care for stranded children”. They have also been told there could be disruption to supplies of food and fuel if the amount coming into the country is not enough to match demand.

Schools have been advised to speak to suppliers to see if they can purchase food “off contract” and to ascertain whether they have stockpiles sufficient for an emergency. They have been told there is “no legal obligation” to provide hot school dinners and that they can substitute them with cold food or ask parents to provide packed lunches.

Gas supplies are “very unlikely” to be affected, but there could be petrol issues for school buses in the event of panic-buying. However, the council believes the government would take over at this point.

“If the national emergency plan for fuel (NEP-F) is enacted, it is likely that public and school transport would be prioritised,” the document says.

The detailed operation guidance notes are part of the council’s meticulous no-deal planning, which has been under way since last year.

The county decided to act in the knowledge of the impact of congestion on the county’s services and businesses, following road closures for 24 days in 2015 because of a strike in France.

Industry, homeowners and tourist attractions all suffered, with miles of the M20 turned into a lorry park at an estimated cost to the local economy of £1.5m a day.

Ian Hartwright, a senior policy adviser for the National Association of Head Teachers, said Kent’s plan was “considerably more useful” than anything provided by the government.

But he added that “much of the guidance places significant extra burdens on schools” and the capacity of schools to respond “remains to be seen, particularly when school budgets are at breaking point”.

Ian Watts, area education officer at the council, said the county had “a duty to the families of Kent” and “it would be remiss to assume no impact”.