Google has opened its Checkout online payment processing service to retailers in the UK, the first time it has been available to businesses outside the US.

Checkout stores shoppers' personal details such as shipping address and credit card number, allowing them to make online purchases with participating retailers simply by entering their Google user name and password. Google then passes on to the retailer the information necessary to complete the transaction.

The company is also localising Checkout for other countries, a spokesman for Google in Europe said, although it’s not saying yet where the service will be offered next. Expanding the service will put it in greater competition with eBay's PayPal, which offers merchants in several countries a similar payment processing service called Website Payments.

Retailers can embed Checkout payment buttons in their websites or even in online advertising placed through Google's AdWords platform, bringing potential customers one step closer to purchase. Google also allows retailers to offset some of their AdWords spend against Checkout transaction fees.

Google opened the Checkout service to US retailers and shoppers in June 2006, and later gave the retailers the option to ship to customers in other countries. Buyers in 145 countries can access the service, according to Google's website.

Allowing UK retailers to use Checkout was no simple matter, a Google spokesman in London said.

"From a technical perspective, things are handled differently here, things as mundane as how taxes are calculated, or how addresses are formatted," he said.

Consumer electronics retailers Ebuyer is one of the first UK retailers to use the service. (Google's website has a full list of UK retailers using Checkout.)

On Friday, visitors to Ebuyer's website clicking on buttons to buy were led to a page sporting a prominent Google Checkout button, with an offer of a £10 ($19.75) discount on purchases over £30. The discount is a Google offer to UK customers signing up for the Checkout service for the first time before 11 June.

Google also has a special offer for UK retailers: it will waive all transaction fees for the service through 31 December. After that date, it will charge £0.15 plus 1.5 percent of the transaction value, although retailers will be able to process transactions worth up to 10 times their monthly spend on AdWords advertising for free.

To sign up for the UK service, retailers must have a UK bank account and UK address.