Alertr compared the prices for items included in government’s consumer price index (CPI) ‘shopping basket’.

It found Asda to be the cheapest supermarket for the sixth month in a row, while costs at Ocado have risen month to month.

The results have been determined by carefully tracking how each online retailer prices the 43 items outlined in the government’s CPI ‘shopping basket’ on a week-by-week basis.

However, budget supermarkets Lidl and Aldi were not included in the comparison due to the inability for customers to shop full ranges online and not having the same like-for-like branded products the other supermarkets stock.

Asda was overall offering the cheapest items during the four weeks of analysis, with Sainsbury’s coming a close second in week three, with its basket just 42p more expensive than Asda and less than Iceland, the second cheapest supermarket overall in October.

Looking into the pricier supermarkets, Tesco takes the crown as the second priciest supermarket analysed, while the cost of a Morrison’s basket was 39p less than this time last month.

Despite Waitrose and Ocado stocking many of the same items, the significant difference in basket costs is clear, with Ocado £16.62 more expensive than Waitrose.

The prices of some kitchen staples dropped from week three to week four at Morrisons, with Kenco Millicano coffee falling in price from £5 to £3, Heinz ketchup dropping from £2.50 to £2 and Hartley’s Strawberry jam going from £1.60 to £1.25.

Andy Barr, co-founder of Alertr, said: “Four out of the seven supermarkets are seeing their average basket costs go down each month, but the likes of Waitrose, Tesco and Ocado are consistently rising.

“As we enter a second lockdown, it will be interesting to see whether or not prices rise across all supermarkets over the next month, or if we see further discounts to help cash-strapped consumers likely to be affected further in the run-up to Christmas.

“It is still really interesting to see that Waitrose is staying firmly in the middle despite being known as the more expensive store. Tesco and Morrisons really need to think about dropping their prices if they want to beat even the likes of Sainsbury’s which is proving to be more affordable than ever before.”

Alertr has been tracking the prices of 43 everyday items from the shopping basket on the Office for National Statistics’ CPI since 2019.

Included within the list are items such as eggs, milk and bread, as well as non-perishables like pasta, rice and cereal.

The full breakdown of supermarkets average basket costs from lowest to highest over the four-week period in October were as follows:

1. ASDA – £128.16 – £2.20 less than last month
2. Iceland – £131.31 – £1.09 less than last month
3. Sainsbury’s – £132.84 – £2.40 less than last month
4. Waitrose – £139.60 – 10p more than last month
5. Morrisons – £141.14 – 39p less than last month
6. Tesco – £145.17 – £5.53 more than last month
7. Ocado – £156.22 –  £4.98 more than last month