There are fears of major backlogs involving lorries and goods at ports such as Dover if there is no longer frictionless trade with EU nations.
The Observer, citing Freedom of Information details, claims 14 military planners have been deployed to ministries including the Department for Transport (DfT), Home Office and Foreign Office as well as the Cabinet Office – the hub of the government’s Brexit planning.
The DfT has already been criticised for giving a £14m contract to run ferries if there is no deal to a company without any ships.
And last week a trial by the government using a disused airfield as a lorry park was attacked by some hauliers as a “waste of time” and “too little, too late”.
Up to 150 lorries were initially expected to take part in the high-profile rehearsal in Manston, Kent, but only 89 were actually involved.
According to The Observer, four planners have been posted in the Border Force, which is facing the challenge of keeping passengers and goods flowing to and from Britain should no EU agreement be signed.
Three are operating in the Foreign Office, while six are working from the Cabinet Office, it claims.
Some departments had asked for assistance on no-deal planning, “recognising the unique skills and operational planning experience the military can offer”, the paper says.
Exercise planning and overall “command and control” advice are apparently their main duties.
Contingency no-deal preparations are taking place under Operation Yellowhammer, with plans drawn up on the assumption that critical trade between Calais and Dover will face disruption, The Observer says.
A Ministry of Defence spokesperson said: “The MoD routinely works with other government departments on planning for a range of contingency scenarios.”
Meanwhile, Liberal Democrat leader Vince Cable has claimed he was told by civil servants about contingency plans to slaughter a third of British sheep if there is no deal.
World Trade Organisation tariffs would hit exports so much there would be too many sheep, causing domestic prices to plummet, he said.
But an environment department spokesman played down suggestions a mass slaughter was on the cards in the event of no deal.