Industry insiders claim that Tesco has inflated the cost of some of its most popular produce to make subsequent price cuts appear more generous.
The claims come as the big four supermarkets squabble in the crucial pre-Christmas trading period about who is cheapest.
Tesco's low-price claims are heavily linked to a promotional campaign which promises 50% off five fruit or vegetable ranges every week.
However, this is not all it seems. The price of loose white grapes was raised on November 19 from £3.98 per kilo to £4.99 - a rise of £1.01 or 25 per cent. Two weeks later - on Monday - the price went back down by £1 a kilo to £3.99.
Tesco launched promotions in its stores and on the internet announcing that it had cut the price of the white grapes by £1 per kilo.
A similar tactic appears to have been used with the staple of the Christmas dinner, Brussels sprouts. Tesco held the retail price for 500g of sprouts at £1 despite the fact that an increase in farm supplies allowed its rivals to charge between 50p and 79p. But this week, it cut the cost to 50p per 500g in a 'half-price' Christmas promotion.
Industry analysts claim the supermarket was able to make the half-price claim only because the original figure of £1 was inflated.
In another example, Tesco raised the price of an 800g pack of Jaffa Clementines, a Christmas favourite, from £1.99 to £2.99 for the first week in October.
Since then it has been running a half-price offer at £1.49 per pack.