Social networking sites account for more than 25% of UK online display ad impressions, according to comScore Ad Metrix.

A study of UK online display advertising on social networking sites showed that the sites accounted for 13.8bn display ad impressions in August, representing more than a fourth of all display ads viewed online.

Telecommunications companies such as Telefonica 02, Deutsche Telekom and BT were the heaviest social networking site advertisers, delivering more than 949m display ad impressions on social networking sites in August, amounting to 7% of all display ads delivered in the site category.

Retail ranked second, with banking brands in third, followed by travel and then entertainment brands.

The study did not specify whether the heavy advertisers were placing recruitment-related ads.

comScore is a leader in measuring the digital world.