From Thorntons shortcake to Nestle chocolate and even Pledge polish: It's the incredible shrinking groceries rip-off

In these straitened times, getting value for money is of paramount importance to shoppers.

But as checkout bills rise, supermarket trollies are actually getting lighter – according to research which indicates major brands and retailers are engaging in "underhand" product shrinking to boost profits.

Many popular food brands have been quietly reduced in size in the last 12 months, with shoppers now getting less for more.

Major brands identified by the consumer watchdog Which? as having increased in price while diminishing in size included producers of sweets, crisps, dish washer tablets, furniture polish and beef burgers.

The survey showed that a pack of Birds Eye beef burgers are now sold with a quarter fewer burgers, dropping from the original 16 to a dozen despite its price increasing by 8 per cent from £3.98 to £4.29 this year.

The watchdog, which reviewed prices and sizes offered in the last 12 months, said products were "getting smaller" with manufacturers conducting systematic shrinkages.

Campaigners have urged supermarkets to produce "clearer, more consistent" unit pricing on food to allow customers to compare prices and identify the best deals on offer.

But brands said the smaller products were a bid to avoid increasing prices. Many manufacturers claimed retailers ultimately set prices but when asked if they had reduced wholesale prices or set lower recommended retail prices on their products, they told Which? they had not or declined to comment.

Richard Lloyd, executive director of Which?, said: "Shrinking products can be an underhand way of raising prices. We want simpler pricing so people can easily compare products to see which is the cheapest, and for special offers to be genuine."

Thorntons Mini Caramel Shortcakes have increased in cost by 10p at Waitrose. The rise comes despite Thorntons now offering only 10 in a pack where previously a dozen were included. The volume of Pledge furniture polish has shrunk by 17 per cent but its price has stayed the same or increased at many supermarkets, the survey said. The chocolate sweet Nestle Munchies is now sold 24g lighter than its original 150g.

Nestle said it had dropped its cost price but would not say whether the decrease was proportionate to the amount its products had shrunk by. Thorntons said reducing product sizes allowed for "better promotions".