https://www.bbc.co.uk/news/business-44613658
Of course, shortages, misunderstandings and accidents could still happen in a planned economy, indeed, Marx reckons we'd have to run a surplus on most goods to keep things ticking over.
The point, however, is that with abatoirs halting operations, businesses running out of stocks, etc. circulation of money will drop, and someone, somewhere will default on a payment, forcing banks to start calling in insurance and loans, with the inherent risk of a full blown panic/crisis appearing out of nowhere.
Part of the point of Marxian crisis theory is that expanded reproduction of capital is an inherently unstable process, prone to shocks.
Add in the slump in investment due to Brexit, and things could turn messy fairly quickly.