London (CNN) Boris Johnson's government has released its "Operation Yellowhammer" planning document, which warns of medicine shortages, severe delays at the Dover-Calais crossing and an increase in food prices if the UK leaves the European Union without a deal.

The disclosure of the document -- which describes a "reasonable worst-case scenario" -- was forced on the government by lawmakers, who voted on Monday to approve its release.

But Michael Gove, the minister in charge of no-deal planning, said the government would not release internal communications between aides about Johnson's prorogation of Parliament, which was also mandated in the bill passed by Parliament.

"As you will also be aware, by longstanding convention under successive Administrations of all political colours, the Government does not release Cabinet and Cabinet Sub-Committee papers," Gove wrote in a letter sent to former Conservative MP Dominic Grieve, who had led to push for their publication.

The Operation Yellowhammer document reports that disruption at English Channel crossings could last up to three months before it eases, with up to 85% of heavy goods vehicles unprepared for new French customs checks that will be introduced on day one after a no-deal Brexit.

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