Claims that online shoppers are being charged different prices by companies using software to detect the wealth of its customers are being investigated by the Office of Fair Trading.

The watchdog has responded to concerns that shoppers using Apple Macs or iPads and visiting top end websites might be charged more.

There are also growing numbers of anecdotal reports that suggest sophisticated systems are being used to raise prices on websites when they detect that shoppers are “emotionally committed” to a purchase. For instance, if someone who is looking at an airline site for flights has already browsed hotel options, it suggests that the search is more than casual.

The software analyses the “trail” of cookies — tiny files unique to a particular website page — on a computer that reveal precisely where a particular shopper has been searching, giving retailers vital information about their preferences. As well as analysing the cookie trail, the “personalised pricing” software can work out the type of computer or device being used and its location. Certain devices — particularly those made by Apple — are associated with higher spending consumers.

IT expert Tom Cheesewright said: “There is currently no hard evidence other than anecdotal that it is happening, but it is certainly technically possible. There are lots of references to it on internet forums and friends are already clearing cookies so they give nothing away.”

The OFT is so concerned about the risk of consumers being overcharged that it has launched a huge evidence-gathering trawl — in partnership with the US Federal Trade Commission — to find out the extent of the practice.

Clive Maxwell, chief executive of the OFT, said: “We know that businesses use information about individual consumers for marketing purposes. This has some important potential benefits to consumers and firms.

“It is important that we understand what control shoppers have over their profile and whether firms are using shoppers’ profiles to charge different prices for goods or services.” The OFT plans to publish its findings in the spring.

Amazon is the only company known to have attempted personalised pricing when it briefly tried it in 2000. It backed down after customers became suspicious.

Andrew Fano, of consultants Accenture, said he believed that at least six of America’s biggest web retailers were already customising prices.

Case study: Holiday price was £120 higher

University administrator Julie Seddon had been searching for a holiday to Turkey with Travel Republic on her home computer, making several visits to the site.

But the next day the price had gone up by £120. Ms Seddon, 54, booked because she thought it was set to sell out for the weeks she wanted. She checked again on her office PC, which did not have the cookie trail showing her interest. It was back to its original price.

She said: “I rang Travel Republic, who initially said that prices change as people book and that was why it was higher. So I asked them to explain how I could go on a different PC and get a lower price.”

Ms Seddon was told one price was for when payment was made in full and one for when there was an initial deposit paid. But the site did not reference this and the company let her rebook. Although the incident does not prove differential pricing software was used, Ms Seddon remains suspicious that such a large price change could be triggered by a different computer.