A no-deal Brexit could lead to six months of chaos on key cross-Channel routes, the latest UK Government assessment shows.

Ferries between Dover and Calais and traffic using the Eurostar Channel Tunnel service could be disrupted until the end of September 2019.

READ MORE: MPs warn 'real prospect' of major disruption at UK ports if there is no-deal Brexit 

A letter sent by Matt Hancock, the UK Health Secretary, to the pharmaceutical industry and NHS contained the warning.

He said: "Although we cannot know exactly what each member state will do with respect to checks on the EU border, the cross-Government planning assumptions have been revised so we can prepare for the potential impacts that the imposition of third country controls by member states could have.

"These impacts are likely to be felt mostly on the short straits crossings into Dover and Folkestone, where the frequent and closed loop nature of these mean that both exports and imports would be affected.

"The revised cross-Government planning assumptions show that there will be significantly reduced access across the short straits, for up to six months.

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"This is very much a worst-case scenario; however, as a responsible Government, we have a duty to plan for all scenarios," he explained.

UK ministers are drawing up plans to fly in vital drugs and give priority to lorries carrying medical supplies at gridlocked ports.

Paul Carter, Kent Council's leader, called for emergency measures to prevent lorries entering the county to avoid chaos on the roads.

"We now need far more input and information from national Government in how they are going to work with us," he insisted.

"There must be a national freight transport plan which, when necessary, can hold lorries back from coming into Kent in the first place should the need arise."

With the Commons vote on Theresa May's Withdrawal Agreement expected to result in it being rejected by MPs, the risk of a no-deal Brexit could increase.

Meanwhile, the Border Delivery Group, a Whitehall co-ordination group for Government departments that have an interest in border issues, has been holding discussions with key stakeholders today.

The discussions centre on "the Government's no-deal planning assumptions for the border", the PM’s spokesman said.

READ MORE: Your Brexit plans will not solve Irish border issue, Theresa May tells critics 

Elsewhere, leaked Government papers suggested that Ireland could suffer more from a no-deal Brexit than Britain with a projected seven per cent drop in GDP compared to five per cent for the UK.