The supermarket chain is considering introducing banking into its services, which could offer savings accounts in addition to existing insurance and credit cards.

Combining bank and supermarket data would be unmatched in tailoring messages to specific people, marketers say.

''With this data, retailers would know absolutely every movement we had, and then they could target us effectively,'' founder of Pulse Marketing Lauren Fried said.

Privacy experts say there are no laws that would stop Coles from combining its data on shoppers and bank customers to target them with very specific offers and promotions. ''It's a serious concern if they are cross-leveraging between one another, taking advantage of customer data,'' said Roger Clarke, chairman of the Australian Privacy Foundation.

If the data falls into the wrong hands, that is very concerning, one leading data analyst said.

''It could lead to individuals being identified on the basis of controversial purchase choices such as political-leaning magazines, leisure pursuits or club memberships. Consumers need to be aware of the potential dangers.''

But a Coles spokeswoman said there were no privacy concerns.

''We do not share or sell the personal information of members outside of flybuys,'' she said.

Woolworths recently said in an industry publication that it had managed to ''overlay'' its insurance company's car crash data base and its Everyday Rewards statistics to reveal which type of consumers were best to target for insurance.

Customers who bought red meat and milk were found to also have lower car insurance risks, Woolworths director of group retail services, Penny Winn, told AdNews.

To make the best use of its data, Woolworths recently partnered with data analytics company Teradata, to record daily point-of-sales and integration of ''continuously rising volumes of detailed customer data'', its website says.

In May, the chain bought 50 per cent of data analytics company Quantium, which sells de-identified data to other companies.

Legal experts say there is no law to stop banks accessing supermarket data. ''There are privacy concerns about banks in general anyway and about supermarkets. And if Coles becomes both … I don't see that the law stops that from happening,'' said Alan Tyree, an expert on banking law.

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