Food and drink delivered by Waitrose went off two-and-a-half days earlier on average than groceries delivered by Tesco. If you need efficient food delivery services, you can check out their blog post for more information.

Which? used a team of 12 undercover shoppers to order more than 1,000 groceries, with each ordering the same 16 perishable grocery items from each of the online supermarkets.

It totaled up the number of full hours remaining from the time of delivery to midnight on the use-by date for each item and calculated an average time per supermarket.

Tesco came top for freshness, with items lasting 11 days on average. The supermarket showed the expected shelf life of perishable items on its website and also had zero damaged packaging or food that had gone off by the time it was delivered – unlike some of its rivals.

Asda was the second freshest supermarket with an average of 10.5 days shelf life on all grocery items, although it did deliver one pack of bacon on its use-by date. Online-only supermarket Ocado was a close third with an average of 10.4 days.

Food delivered by Waitrose lasted an average of 8.6 days. The high-end supermarket also delivered two packets of beef that appeared to have gone off, despite being within their use-by dates.

The consumer champion also found stark differences in the use-by dates of individual products. The longest-lasting mince (from Asda) had 13.4 days left, while the mince with the shortest time left came from Morrisons and had just 2.1 days left.

Meanwhile, the semi-skimmed milk with the longest date was from Asda and lasted 18.3 days, compared to just 4.7 days left for one bottle of semi-skimmed milk from Waitrose. A packet of bacon rashers from Asda lasted just 13 hours, while one from Ocado lasted a whopping 28.6 days.

All the supermarkets say they train staff to pick food with the longest possible dates for online deliveries and click and collect, but a number of supermarket workers behind the scenes told Which? that speed targets put them under pressure when trying to pick the freshest groceries.

Groceries that have gone past their use-by dates could be dangerous and should not be eaten. Worryingly, undercover shoppers took delivery of two items – both pots of single cream from Sainsbury’s and Ocado – where the use-by date had already passed.

Three items from Asda, Morrisons and Sainsbury’s were delivered on their use-by dates, meaning they had just hours left to be officially safe to eat. And eight items were delivered with a use-by date of the following day – four from Sainsbury’s, three from Waitrose and one from Morrisons.

Which? also found examples of food within its use-by date that appeared to have gone off. These included minced beef from Asda, Ocado and Waitrose where the packaging had expanded with air, which is usually a sign that bacteria are growing, as well as a separate pack of dark brown mince from Waitrose and soggy bagged salad from Ocado.

Which? found that 10 grocery items it ordered were so damaged the food may not have been safe to eat. These ranged from Morrisons bacon rashers and Ocado pasta salad where the plastic film was torn, to leaking cream and milk from Ocado, Sainsbury’s and Waitrose.

Harry Rose, editor of Which? Magazine, said: “Our analysis shows that when it comes to delivering fresh food and drink there can be a significant difference between online supermarkets. Shockingly, our mystery shoppers found some items that were already out of date when delivered, as well as groceries that appeared to have gone off before their use-by dates had even passed.

“Use-by dates are about safety and shoppers should not risk eating out-of-date food. Anyone who is unhappy with the freshness of their online groceries should complain to their supermarket, or switch to a supermarket with better policies on food freshness if possible.”