The cost of own-label canned food in the big four has soared in the past month, flying in the face of ongoing Tesco and Sainsbury's campaigns promoting own-label brands as cheaper alternatives to branded goods.

Although canned food brands were also up in price because of the rising cost of raw materials, the prices of own-label tinned lines have risen far more sharply.

The big four increased the prices of their cheapest own-label baked beans by 61% to 29p from 7 October to 4 November, according to figures from The Grocer 33 price survey.

The price of Heinz Beanz (415g), however, rose by an average of just 8.2% to 56p across the big four last month, while a 400g tin of Heinz cream of tomato soup remained at an average 68p.

Sainsbury's Basics tinned spaghetti in tomato sauce (420g) has soared 57% to 22p, and red kidney beans (420g) rose 50% to 18p. Morrisons Value tinned spaghetti (420g) was also up 57% to 22p.

However, the 40% average price rises for own-label tuna were matched by similar hikes on branded lines, according to a leading canned supplier.

Asda and Tesco predicted costs would soon come down and said that once they had, they would pass on those savings.

"Generally, we are seeing food price deflation across the board, which is good news for customers," said an Asda spokeswoman.

In September, Tesco and Sainsbury's caused outrage among branded suppliers by launching high-profile campaigns encouraging customers to switch from brands to own label.

Tesco has since claimed its online tool Cheaper Alternatives has persuaded half its online customers to trade down from branded to own-label lines.

"Customers are switching to the service, but also customers new to the site are giving it a try," said Mandy Minichiello, senior marketing manager at Tesco.com.

Sainsbury's and Morrisons refused to comment on the own-label price increases.