I suppose one could come up with really bad scenarios even for a really bad crash out so I will try to go middle of the road.
Similar to the 1973 oil crises, you could probably expect long lines at petrol stations with perhaps strict limits on much petrol you could buy.
Food will probably be available but you may be limited by the store as to how much you could buy. It may well be that the food available is simply not to your liking or fairly unhealthy like tinned peaches drowned in heavy syrup.
If you go to the store to get say milk and bread it may not be available but cereal is. When milk and bread are available cereal may not be.
You may have to engage in Soviet-style shopping buying whatever is available when it's available because it may be sometime before you see it again ( soap, shampoo, nail polish, toothpaste, etc ).
Checking out the oil embargo on Wikipedia I came across this nugget:
" Despite being relatively unaffected by the embargo, the UK nonetheless faced an oil crisis of its own—a series of strikes by coal miners and railroad workers over the winter of 1973–74 became a major factor in the change of government. Heath asked the British to heat only one room in their houses over the winter. The UK, Germany, Italy, Switzerland and Norway banned flying, driving and boating on Sundays. Sweden rationed gasoline and heating oil. The Netherlands imposed prison sentences for those who used more than their ration of electricity. ".
With a further, perhaps rather drastic decline in the pound, petrol, heating oil, electricity, and food will be rationed but perhaps not in the traditional sense but according to availability and especially price.
Most people will probably be okay at first, but when they realize that all of this will be their new life for the foreseeable future with no end in sight, then they will become more and more angry and bitter with a consequent rise in radical parties of both the left and right.
There probably won't be large-scale riots but rather pub brawls and isolated street fights.
Whatever the faults and flaws of the UK in the EU, it will become by comparison a heaven of times past as opposed to the new harsh reality.
Okay, that's my middle of the road scenario which is quite dreadful enough, hopefully the WA gets passed through so the UK can experience some degree of relative normalcy at least for a while.