Few Christmas foods have been spared from price inflation this year, but one item dwarfs the rest of its trolley mates when it comes to rocketing prices - the peanut.

A study by The Grocer of 251 bagged peanut products stocked across the top five multiples shows prices have soared by 25.5% to an average of £9.20/kg over the past 12 months. Peanut butter rose by a similar 26.8%, to £6.82/kg.

The five-year retail picture is even worse for nut lovers. Since 4 December 2008, peanut prices have risen by 99.1% from an average of £4.62/kg to £9.20/kg.

Controversially, shoppers are having to pay more for their nuts even though wholesale peanut prices have actually come down recently. Bad harvests meant peanuts became a lot more expensive last year - peaking at £1,568.5/tonne in January 2012 - but since then prices have eased off to about £1,1130/tonne [Mintec].

Rising crude oil prices tend to be followed by rising plastics prices, but - as our tracker shows - not all packaging materials have moved in line with crude this year.

While the cost of LDPE and HDPE have increased by a respective 17.9% and 5.1% in response to higher oil prices and increased demand over the past year, PET has fallen 23.1% over the past 12 months and a 1.9% in the past month.

PET prices have fallen despite higher oil prices because they were unusually high in 2011, when soaring demand for polyester fabric pushed prices up. This year, they have returned to more normal levels.

Overall, prices are down for all but three of the 10 items in our tracker, with lower demand because of the economic downturn in many parts of the world a key driver. Testliner prices in the UK are down 12.3% on last year, with cartonboard, polystyrene, Kraftliner and steel also cheaper than they were a year ago.

However, lower wholesale prices have not been passed on to shoppers. The price of a 300g bag of KP Dry Roasted Peanuts cost £1.48 last year, but this year it will set consumers back £1.99 - an increase of a whopping 34.5%.

A UB spokeswoman said the company did not control the price of its products in-store. “That is determined by individual retailers,” she said.

The peanut market had experienced significant inflation in the past few years, driven by “a combination of global supply/demand imbalance, crop failures, migration to competing crops and market speculation”, she added.

Mintec analyst Mark Kozlowski stressed the cost of peanuts at wholesale level was just one factor behind the price at retail counters. “The wholesale costs are important, but processing, transportation, packaging, profit margins and branding costs will all play a role in producing the retail pricing,” he said.

Nut fans keen to avoid paying more this Christmas could opt for other nut varieties, such as walnuts, pistachios and cashews, which have been more resilient to inflation. At £13.81/kg, cashew nuts cost the same as they did 12 months ago, while walnuts have fallen by 5% year-on-year to £9.21/kg, and pistachios are 11% cheaper, at £33.41/kg [BrandView.co.uk].