AdCenter is the arm of MSN responsible for its advertising services.
Advertisers invited to access AdCenter's APIs will be able to add their campaign content directly to AdCenter, or to develop new programs for the purpose.
AdCenter already operates a similar model in the US, where advertisers can register their interest in the hope of being invited to access the APIs.
A number of large companies, including eBay, are currently testing AdCenter APIs in the UK. Other companies will be invited to register their interest when the UK service is launched in full at the end of 2006.
James Colborn, search strategy product manager at Microsoft, said that the software giant had no plans to change its model and introduce Google-style fees to access AdCenter APIs.
Colborn hoped that opening up the APIs in the UK would benefit both Microsoft and the UK advertising industry, and that advertisers could help Microsoft to learn about the market.
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