Inflation is an obvious menace when prices are rising, but a more insidious form is finding its way into our trolleys the prices are staying the same, but the items we buy are shrinking. That’s shrinkflation.

Manufacturers and retailers are increasingly sneaking in new reduced sizes while describing them as special offers or re-launches.

Consumers do not like it. Research by lobby group Which? found 58 per cent of consumers in the UK would rather pay more than have goods downsized. Shrinkflation has taken some of the crunch out of a packet of Walkers crisps. The cost has stuck at 49p but the contents have fallen by six per cent from 34.5g to 32.5g.

A Mars bar, selling at 59p, has shrunk 2.5g to 58g. The shrinking has happened over the past few years, with many customers being none the wiser.

Cadbury is another culprit. It made a big boast of product redesigns two years ago, but failed to mention that products would shrink at the same time. It cut the number of chocolates in a Roses tin by a typical 11 treats, for instance, with the weight falling from 975g to 850g.

Housewife Laura Kirby, 31, shopping at a local supermarket with children Fletcher, three, and 19-month-old Dexter, is angry at the phenomenon.

She says: ‘Because I get the same things every time I actually notice my shopping bag getting lighter. But the bill is the same.’

She adds: ‘Most of the shrinkage is around foods where there may be obesity worries chocolate and crisps as well as breakfast cereals. Food manufacturers are clearly exploiting a consumer weakness.’

Food firms are also cutting the number of items in a packet. Which? points out a cereal such as Shredded Wheat Superfruity that used to be sold for GBP2.68 at Sainsbury’s was put on GBP2 special offer before returning to GBP2.68 but with less content.

A Which? spokeswoman says: ‘You need to be eagle-eyed when shopping. It shows the importance of going through shopping bills and scanning the shelves for better value maybe switching brands.’

A spokesman for PepsiCo, which owns Walkers, said: ‘We have faced rising commodity prices and raw ingredients costs. Where possible we absorb costs but we have had to make slight reductions to the weight of some crisp products.’

Nestle said: ‘Occasionally we make changes to the size, driven by factors including anything from product reformulation, changes in packaging or ingredients costs.’ Similar excuses for shrinking the size of goods were put forward by confectionery manufacturer Mars and Kraft-owned Cadbury.