There is more pressure on Australia’s big supermarkets as a scathing report reveals soaring prices at the checkout, a lack of competition and customers losing trust in specials and discount schemes.

The Australian Competition and Consumer Commission released its interim report on supermarkets on Friday, laying out issues in the sector as it looks to make the weekly shop fairer for consumers.

While the report did not detail recommendations, commission deputy chair Mick Keogh said there was concern about how major supermarkets were abusing their powers.

“Oligopolistic market structures can limit incentives to compete vigorously on price,” he said.

“We see Woolworths and Coles providing a broadly similar experience to customers through largely undifferentiated product ranges, pricing at similar levels and similar non-price offerings including loyalty programs.”

The supermarket inquiry took information from more than 21,000 shoppers, a record for an ACCC consumer survey.

The report found most low-income households had to spend 20 per cent of their pay on groceries, while the cost of a typical basket of goods increased by 20 per cent in the past five years.

Keogh said customers across the board faced difficulty when trying to compare prices, and some felt forced to join loyalty programs and hand over personal information to get cheaper prices.

“Many consumers have told us that they are losing trust in the sale price claims by supermarkets,” he said.

“These difficulties reportedly arise from some of the pricing practices of some supermarkets, such as frequent specials, short-term lowered prices, bulk-buy promotions, member-only prices and bundled prices.”

The report’s release comes days after the consumer watchdog said it would take Coles and Woolworths to court over claims of misleading specials, alleging the chains increased prices only to then reduce them for promotions in which they were still dearer than the original cost.

Coles and Woolworths make up 67 per cent of Australia’s supermarket sector, with the interim report also noting the considerable time it had taken the next largest chain, Aldi, to increase its market share – 20 years to get to 9 per cent.

“Planning and zoning laws may slow a supermarket retailer’s ability to develop new stores by creating additional costs or adding significant delays,” Keogh said.

Prime Minister Anthony Albanese said the federal government would examine the report closely.

“Customers don’t deserve to be treated as fools by the supermarkets – they deserve better than that,” he said earlier this week.

“My government is taking a range of actions to make sure Australians are paying a fair price at the checkout and Australian suppliers are getting a fair price for their goods.”

Public hearings are expected to be held in October and November before the final report is handed to the government by the end of February.

Aldi prevails in price comparison

It follows a report on Thursday that reaffirmed Aldi as Australia’s cheapest supermarket, despite its struggles to break into the local grocery scene.

Research from consumer group Choice found the German-owned grocer to be at least $16 cheaper than Coles and Woolworths across 14 common food items, but was dismissed as a “very narrow basket” by the Australian Retailers Association.

But AAP analysis across a wider shop – including cleaning products, personal hygiene items and other family staples along with meat and vegetables – corroborated the Choice findings.

AAP’s 13-item basket cost $72.90 at Aldi, compared with $80.20 at Woolworths and $89.25 at Coles.

Items such as a 44-pack of nappies ($11.50), a can of tomato soup ($1.10) and Scotch Finger biscuits ($1.25) cost the same at all three retailers.

But Aldi had cheaper steak, olive oil, lettuce and tampons, to produce the most cost-effective shop.

Released on Thursday, Choice’s data found Aldi’s basket cost $50.79, noticeably cheaper than Coles ($66.22) and Woolworths ($68.37).

ARA chief executive Paul Zahra said Choice’s analysis was “not a fair or useful comparison” given it could be comparing premium brands with Aldi’s private label options.

But AAP’s analysis relied on the cheapest available price – including Coles’ and Woolworths’ own-brand items – across a wider range of products.

The ACCC also found half of the respondents to its consumer survey compared prices “always” or “most times” before shopping, way up from 17 per cent in 2008.

-with AAP