Google has approached the European Commission for permission to acquire online advertiser DoubleClick for $3.1bn (£1.55bn).

The potential deal has been referred to competition watchdogs across the world because of concerns that it could give Google too much control over online advertising.

Google has already filed with the U.S. Federal Trade Commission and with the Australian competition regulator.

Financial analysts estimate Google is paying an estimated 52 times the predicted value of DoubleClick.

DoubleClick connects ad agencies, marketers and web site publishers and has more than 1,500 corporate clients.