Agreed. I wouldn't be surprised to also see violent revolt ensue as well. Not advocating for it at all, but I have a feeling that NOT all Brits are as passive and pu$$ified as the "Governing Authorities" believe they are.
Already in place here. Furs, gold, fish, eggs, lumber etc.; and of course services of all kinds. I have paid, been offered or accepted all of these instead of currency.
Our mechanic maintains our truck, PR grooms and oversees the veterinary care of his dog. Other people trade fish or wild harvested meat (Moose, venison, goose etc.) for boat repairs, carpentry, house and lawn maintenance, welding...you name it.
Of course we use credit and debit cards too for routine purchases and bill paying. Nevertheless, there is a very active barter economy where I live.