Not aware of any supermarkets offering this, and it’s not because they haven’t thought of it. Products can change specification so that a product that was, for example, dairy free, now includes dairy, or vice versa. Even if the info on the system is up to date, which there is no guarantee of with branded lines (as the retailer doesn’t own the specification and is reliant on the manufacturer to tell them about any changes), if a product has changed recently you could have a situation where the system thinks a product is now dairy free but what’s on the shelf is the old recipe. A retailer wouldn’t want to give the impression of promising that all the products in your order will be dairy free when that situation could arise, because it may give you a false sense of security around checking packaging that could lead you to eat something you’re allergic to.