According to The Guardian, Havas spends over $200 million annually with Google on behalf of its clients.
According to one U.K. marketing consultant,
"Google will be eager to avoid this cascading."
I am officially skeptical that this will do any such thing. I think it's highly unlikely that Martin Sorrell (WPP) and his pals at Omnicom, IPG and Publicis will give up the huge revenues they generate from Google ads for high-minded principles.
They'll make noise, but they won't risk 5¢ unless their clients force them to.
Meanwhile, here in the U.S. agencies and marketers don't seem to give a damn where their ads run just as long as they're cheap.