The Government’s Pricing Practices Guide (PPG) states that product comparisons should “in general” be made with the immediate previous price for the product. If this cannot be done, the basis of the comparison must be “explicit”.

Which? highlighted several examples of places where it believes the guidelines were breached. It says a “was” price must be the most recent price the item was sold at for 28 consecutive days or more and not a price that is more than six months old.

In one case, it said AO listed a Bosch washing machine for £399 “was £539” - the price it had been for 19 days the previous year instead of the £499 it was in the months before.