Retailers slavishly toe the party line on the subject of e-commerce. “Online retail complements shopping in person; it is not a threat,” they recite in unison.

However, OC&C found a clear correlation between the amount of shopping that is done online for a particular product and the profits of retailers.

While internet sales are growing, it is the products that are relatively ill-suited to online shopping that have the best margins.

Clothing and footwear boast healthy margins, but online sales remain as a small percentage of overall sales because of the reluctance of shoppers to buy items they have not tried on and their objection to the cost of postage and packaging.

Richard McKenzie said: “In most categories where there's a significant proportion of online sales, the major online players are cheaper than the high street. Inevitably, the high street players have to respond because their customers are comparing prices. That, in turn, will push into their margins.”

It raised questions about high street retailers' strategies, Mr McKenzie said. Physical retailers would have to start charging different prices at their online operation and their high street stores. “They need to be clever. You have to be more flexible about pricing. This was the rationale for DSG taking the Dixons name and putting it online. They have a price-competitive brand.”

It is an article of faith among some retailers that pricing is uniform between stores and websites. Many say that consumers increasingly are researching their purchasing decisions online, essentially using websites as a showroom, before buying items from a physical shop. Small retailers are increasingly dispensing with the overheads of a bricks-and-mortar address and taking their operations online. Mr McKenzie said the challenge was that each business model needed different methods to succeed: “A store appeals to people within a mile of the store, a website appeals to people all around the country. Moving online is not going to be a panacea.”

A glance at Britain's 20 biggest retailers reveals a mix of listed companies, groups in the hands of private equity, such as Boots, foreign-owned chains, such as Asda, and family- owned businesses, such as River Island. Performance varies across ownership models. Foreign-owned companies fared worst, with margins of only 2.1 per cent and profits declining by an average of 1.3 per cent annually.

Family-owned or family-dominated companies enjoyed margins of 5.6 per cent, while for listed companies that figure was 4.5 per cent. The findings suggest that private equity-controlled groups perform in line with listed companies, a conclusion that may trouble the private equity industry since it specialises in turnarounds.

“The figures show that private equity managers are human as well,” Mr McKenzie said. “Some of the businesses they have taken over are in difficult positions.”

American Golf and eBuyer are two private equity-owned businesses that have undergone a sharp improvement in profitability.

The success of companies owned by families also defies the stereotype of the sedate family business muddling along and resistant to change.

“Retail is quite an intuitive game. It's incredibly valuable if you have someone who's been in the market for 40 years,” Mr McKenzie said.

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