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A leaked government document has warned that Britain faces potential "consumer panic" and possible food shortages within the first fortnight of no deal Brexit.

The Whitehall slide entitled "What this could look like on the ground" and marked "Official Sensitive" also warns of gaps in security within weeks of leaving the EU without a deal.

It talks of large numbers of UK citizens returning from European countries because they don't have the right to stay there and talks of the pound settling at a much lower level.

The internal memo, which was obtained by Sky News, is marked: "For Discussion - Not Government Policy".

And the document, which was prepared in the final weeks of then-prime minister Theresa May's time in office, has only been seen by certain cabinet ministers.

Its publication comes as the new government has massively ramped up planning for no deal - including a commitment from the Chancellor of an extra £2.1billion for contingency planning.

And today Treasury Minister Rishi Sunak refused to rule out an emergency no deal budget before 31st October.

The internal document says that from day one "trade and passenger flows from the UK to EU slows" because of "additional process at border", adding that "UK vessels could no longer have access to EU waters and vice versa".

In Northern Ireland, cross-border agricultural trade would "virtually stop" with other trade slowing.

It added that the legal basis for the single electricity market between the Republic and Northern Ireland "falls away".

Within the first fortnight, the document warns of "potential consumer panic and food shortages, even in areas which are not directly affected at the border".

It adds that there could be "possible friction at sea between UK/EU fishing vessels".

Within the first month, small businesses in Northern Ireland "face distress and potential law and order challenges".

(Image: Daily Express)

It says UK nationals living in EU countries could be unable to meet EU member state residency requirements and "may start returning to UK, or ask government for help".

By the end of the first month, security could be more challenging with "heightened policing resource unsustainable, operational gaps continue to emerge".

It also says the pound could settle at a lower level and points out that analysis by the Bank of England "suggests near-term business disruption likely".

It adds: "This could result in demand for support through Kingfisher", one of the programmes drawn up by officials to boost the economy after Brexit.

A government spokesman told Sky News: "We do not comment on leaked documents."