The makers of Mars Bars have been accused of 'shrinkflation' – cutting the size of some by nearly a quarter without dropping the price.

Retailers say they began noticing in March the confectioner had cut single bar sizes from 51g to 40g - without lowering wholesale or suggested retail pricing.

The claims are supported by figures from a leading wholesaler showing the 51g version – appearing as 'discontinued' - carried a 75p price-mark and gave stores 24.24% profit on return.

The new 40g version carries the same 75p price-mark and 24.24% profit on return for stockists.

Jim Moorhead of Top Cards in Livingstone, Renfrewshire, told Better Retailing: "I have just bought a box of Mars Bars and was shocked to discover they have reduced their weight by 21.5%.

"I think they should be ashamed of themselves, yet again, the small business owners are being screwe.

''We'd have to price them at £2 to get the equivalent profit increase as the manufacturer."

Another shop owner reacted, stating: "What kind of joke is this?"

A Mars Wrigley UK and Ireland spokesperson said: "At Mars Wrigley, we're committed to delivering high-quality snacks consumers enjoy. Recently, we made select updates to our bar sizes and pack formats to ensure a consistent supply to our retail customers.

"Consumers will find a range of pack formats – from on-the-go to sharing occasions – designed to reflect new ways consumers are snacking, as well as the need for affordability.

"At Mars, we will always offer our high-quality snacks at the best possible value for money. As part of our work to update our pack formats, we also increased the number of products in our portfolio under 200kcal per single serving by updating bar sizes.

"Mars and Snickers bars are now slightly smaller. While retail pricing is set by individual retailers, our priority is always to provide the great-tasting treats consumers know and love, at prices they can afford."