Egg prices have shot up 40% over the past year as commodity hikes have taken their toll on one of the cheapest proteins available to cash-strapped shoppers.

This time last year, all of the big four were selling at least one six-pack of eggs for less than £1. Today, just Asda and Morrisons offer sub-£1 eggs and the average price of a value pack at the big four is 40% higher than it was last year.

A pack of six Asda Smart Price eggs from caged hens now costs 98p, up from 69p last year, while six Morrisons M Savers eggs cost 99p, up from 65p.

Sainsbury’s is offering a pack of six Basics own-label Freedom Foods-endorsed barn eggs for £1, compared with 79p last year, and Tesco is selling its cheapest pack of six eggs for £1.09, also up from 79p.

Price increases have been especially dramatic on budget egg lines, but other parts of the egg category have also become more expensive.

Of about 130 comparable hen egg lines at the top five, 68.7% are now more expensive than last year, 16% are the same and just 15.3% are cheaper.

Overall, the average unit price of a pack of hen eggs has increased by 8.2%, to a base price of £2.10, over the past 12 months [].

The retailers said higher input costs had pushed up prices. “Factors such as the rising commodity costs of wheat and soya mean that some products, including eggs, have increased in price slightly over the past year,” said a spokeswoman for Tesco.

This was echoed by Sainsbury’s. “Increasing wheat and soya prices mean that, in common with other retailers, we’ve had to increase the price of some of our eggs,” said a spokesman.

Morrisons added that new EU rules on battery cages, which came into force in January 2012, had also pushed up prices.