Worst case contingency: civil disorder could start from early January
(I hadn't expected a significant risk before mid-March)
https://www.theguardian.com/politics/2018/sep/09/sajid-javid-refuses-to-rule-out-disorder-in-case-of-no-deal-brexit
Sajid Javid has refused to rule out the possibility that a no-deal Brexit could cause a sharp rise in crime and widespread protests escalating into weeks of civil disorder, saying it was important that police prepare for any such eventualities.
Contingency plans for a no-deal departure drawn up by the National Police Coordination Centre say shortages of medicine could “feed civil disorder”,
while more general price rises could prompt “widespread protest which could then escalate into disorder”.
The document, leaked to the Sunday Times, cautions that
there could an increase in crime, notably theft and robbery, amid shortages of food and drugs, as well as the “expectation that more people will become ill”.
It says the primary concern would be a shortage of food, medicines and other goods leading to “civil disorder leading to widespread unrest”.
This could last for up to three months either side of the departure date next March, the report says,
raising the “real possibility” that soldiers would have to be deployed on the streets, even with police leave postponed.