An unsettled Brexit poses risks to the NHS and nursing homes, despite extensive government planning, says one observer.
The National Audit Office commended the government for the "huge amount of work" that had been done, but said there were still "significant" gaps.
The extra transport capacity that the government was buying to take drugs to non-Dover ports may not be fully ready by October 31.
And there was no clear evidence that the health care industry was ready, the NAO said.
The report raises concerns that the industry has not received sufficient government support.
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The government organized the supply stock for the NHS.
However, for the relief sector, which is fragmented by 24,000 service companies, no central agreement has been made to store equipment and supplies such as syringes and needles, mostly from or via the EU.
However, when it comes to medicines whose offer has been organized for the NHS and the care sectors, the report acknowledges the work that has been done.
This includes stocking up on drug supplies for six weeks and arranging for the rapid supply of emergency supplies – some drugs, including cancer treatments, have a short shelf life and therefore cannot be stored.
But the report says it is not yet known exactly what level of storage exists.
More than 12,000 medicines are used by the NHS and about 7,000 are from or via the EU.
The report is published after parliamentarians tried to prevent the government from leaving the EU without a withdrawal agreement.
Legislation has been passed requiring the government to request an extension if an agreement cannot be agreed.
Labor MP Meg Hillier, who chairs the Public Accounts Committee, said the report was "deeply worrying."
"I've seen countless examples of missed deadlines and government bankruptcy," she said.
"If the government gets it wrong, it could have the most serious consequences."
Layla McCay of the NHS Confederation, which represents managers, said the planning was detailed, but the situation is still worrying.
She also warned that it was the "unknown and unknowable" who were perhaps at the greatest risk.
A spokesman for the Department of Health and Welfare said, "We want to reassure patients that we are doing everything we can."
He said the government and industry "have set an unprecedented response in preparation for Brexit" with inventories "increasing every day."