Proving it was a "policy" would in practice be impossible.

Mistakes are no excuse in law. Failing to accept the customers' reminder will. So will a climate of repeated "unfortunate oversites".

News travels - anyone who thinks there is no such thing as bad publicity need look no further than Tesco. Or Grenfell Tower!

One thought I have is that special weekend prices could be higher with little or no latency contention. And I can imagine that being first into the affray, starting with loss-leaders like coffee. Which might suit many low-pay zero-hours contractors a lot more of the time. Reality is never simple nor binary.

And I always thought there was a clear legal pricing framework for shops that give the shopper the task of finding the goods themselves. viz the Price Marking Order 2004;

Anyone ever seen smaller glass jars of coffee on offer "cheaper per" than refills in foil? Should we call it mug-bet pricing? The reason they are legally required to show "price per"!