Tesco announces new price comparison coupons deal

Tesco has announced a deal that it claims is the UK's first automatic price comparison coupon. The supermarket will automatically compare the price of a large number of goods in your basket with those at three other supermarkets. If you could have bought them cheaper elsewhere, you'll automatically get a coupon for the difference.

So is this something genuinely new? Can you now guarantee your shopping is always cheaper at Tesco?
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