Swapping to Aldi from the main supermarkets can slash the cost of a weekly shop by almost 40%, according to a survey carried out by The Grocer.

The bill at Aldi for a trolley of 33 items including fresh fruit & veg and meat, bread, milk, wine, cheese, snacks, shampoo and cleaning products came to £34.92. A similar basket at the top five averaged £57.50 - 39.3% more than at Aldi.

However, as the supermarkets offered more branded items and a wider variety of produce, The Grocer carried out a second shop to provide a purely own-label comparison. Where available, we used the basic ranges available at the supermarkets.

That basket also saw Aldi come out on top, at £30.66, swiftly followed by Lidl at £33.19. Overall, Aldi was 16% cheaper than Asda, 20% cheaper than Tesco and 40% cheaper than Waitrose.

“I’m not hugely surprised as we are familiar with this sort of result,” said joint group MD Matthew Barnes. “We have intense sampling sessions twice a week to get our own-label products to where the brands are in terms of taste and performance,” he added.

Joint group MD Roman Heini said Aldi was a growing threat to bigger rivals: “Aldi has changed, and a lot of customers have realised this.”

On Monday, Aldi announced it had turned a £56.9m loss in 2010 into a record £70.5m profit in the year to 31 December 2011. It plans to add 40 new stores to its 470-strong estate next year and recruit 4,500 new staff.

“The Aldi breakthrough, promised for so long, appears real this time,” said Investec analyst Dave McCarthy. “Consumers are accepting that Aldi sells good-quality products at low prices and its long-term plans look realistic and ominous.”