As Campaign revealed earlier this summer (16 June), Mills had been formulating launch plans with two other Carat executives - the former marketing director, Jenny Biggam, and the head of media, Mark Jarvis.
The agency, which takes its name from a pub in Holborn near Carat's headquarters, is due to launch in the next few days. It is backed by private capital rather than by venture capitalists and has offices in Charlotte Street.
"It's a really exciting challenge launching a full-service media agency in today's market," Mills said. "It's going to be tough but we're working hard with a proposition that we believe is relevant to the challenges advertisers are facing today."
The founders hope their experience will enable them to serve medium-sized clients that do not get the service they need from bigger agencies. Mills' background is in planning, Biggam has experience of direct marketing and Jarvis is a formidable negotiator.