Tesco grocery customers will automatically get the price difference if their shop would have been cheaper at Asda, Morrisons or Sainsbury's. But how does it compare against rival schemes?

The UK's largest supermarket chain has today launched Price Promise, which compares the cost of a basket of branded, own label and fresh food groceries against the same or equivalent products from Asda, Morrisons and Sainsbury's (see our Downshift Challenge tool to cut the cost of supermarket shopping).

Tesco paid double the difference in vouchers in a previous scheme, which closed in 2011 after shoppers made money out of it by identifying cheaper products at Asda first (Tesco axes 'double the difference' MSE News story).

But how does the new deal stack up to its competitors' promotions?

All the supermarkets in the table below include branded products in their comparisons and factor in promotional offers such as buy one get one free and half-price deals.

This table compares their other features to help you get your groceries at the lowest price.

Supermarket price promises compared
Asda Ocado Sainsbury's Tesco
What's the deal? (i) You get difference if not 10% cheaper Difference paid if Tesco.com cheaper Difference paid if not cheapest. In-store only Difference paid if not cheapest
Supermarkets compared Morris, Sains, Tesco, Waitrose Tesco.com Asda, Tesco Asda, Morris, Sains
What do you get paid? Difference + 10% off best other price Difference to Tesco.com + 1p Difference to cheapest competitor Difference to cheapest competitor
Includes own-label goods? Yes Yes No Yes
How many items do you need? Min 8, 1 must be comparable Min 1 comparable Min 1 comparable Min 10, 1 must be comparable
Minimum spend? N/A £40 £20 N/A
Money paid in Asda vouchers Ocado vouchers Sainsbury's vouchers Tesco vouchers
Maximum paid £100/mnth, max 10 claims £10 per shop £10 per shop £10 per shop
Vouchers paid automatically? No Yes Yes Yes
How are vouchers paid? You must claim (ii) Email At till At till/email (if shopped online)
When do vouchers expire? 28 days 14 days 14 days 28 days
Does it work in all stores? To be confirmed N/A - online only In main stores (locals & centrals excluded) In Metros, Superstores, Extras (not Express & Homeplus)
Does it work online? Yes Yes No Yes

(i) Deals based on "comparable" items, where weight and/or size is similar. (ii) Claim via Price Guarantee website from 3hrs after in-store shop, 48 hours after online delivery. Morrisons and Waitrose do not run price promises.

Not as generous

MoneySavingExpert.com founder Martin Lewis says: "While not as generous as its previous double-the-difference price promise scheme – which led to many whoops of joy from MoneySavers, who manipulated it to make decent cash, it is certainly a powerful offering.

"The fact it's on both branded and own label products, and the redemption is automatic, gives it some distinct advantages over the Asda and Sainsbury's schemes, though Asda's payout is more generous. Yet it's not a reason to switch to Tesco.

"However, for existing Tesco shoppers it certainly lessens the reasons to leave. It's also a boon to those who like to use multiple supermarkets to score down their price, as presuming the scheme works as promised, this does that."

Tesco says an "independent external agency" collects price data by doing daily web scans of Asda and Sainsbury's websites, and twice-weekly in-store price-checks at three Morrisons stores, as the latter supermarket does not have a shopping website.

Additional reporting by Jamie Stinson.