Dentsu headquarters Dentsu headquarters. Credit: yu_photo / Adobestock

The terms of the deal were undisclosed, but the transactional value is estimated to be £533 million ($678 million), according to the Guardian. 

The completed takeover comes more than 10 years after Tokyo Stock Exchange-listed Dentsu took over U.K. media group Aegis for nearly $5 billion, the largest-ever deal for a British-based advertising group.