We trust them with our search queries, e-mails, calendar information and, more recently, documents and spreadsheets. Now Google is preparing to keep watch over the holy grail of data protection – bank and credit card information.

From today, UK customers will be able to use Google’s online payment mechanism, called Checkout, to make purchases through participating websites.

The idea is that instead of consumers having to enter payment details every time they buy something online, they can refer retailers to Google, which will hold such information centrally and arrange payment on the site’s behalf.

The service, which will compete with PayPal, already operates in the US, where partner websites include ToysRUs, Starbucks and Timberland, but it has not been available to British customers until now.

The only retailer to sign up so far is eBuyer, a seller of computer parts, but several e-commerce platforms will include the service as part of start-up packages for small businesses.

“For customers it offers a secure way to make payments online," a Google spokesman said. "For retailers, it’s a way of attracting more visitors and achieving higher sales while keeping processing costs down.”

The initial part of the transaction – browsing the online store and adding items to basket – will remain in the hands of the retailer. Then, when the customers reaches the checkout, control is handed to Google, which will require only a user name and password in order to authorise the purchase.

The search company has insisted that the service is safe and compliant with data protection laws in the UK and EU. Security experts said, however, that in trying to make online payment services convenient for the customers, companies could compromise data.

“The issue is always balancing convenience and risk," Gerald Kitchen, chief executive of Secure Trading, which provides protection for online payments, said. "Ease of access is obviously important – the service can’t be too onerous for the customer, but at the same time security is so important and these days the problem is mass compromise, as happened at TK Maxx.”

A Google spokesperson said it was the company’s policy not to disclose where or how it stored information. In any instance of fraudulent misuse, the customer would be reimbursed, the company said.