The agency said that it has resigned the account in order to focus on “other clients and new business opportunities”.
Tesco was a founding client of the independent agency, which launched in 2005, but earlier this month called a pitch for its brand advertising in a bid to reinvigorate its fortunes.
It is using the intermediary Oystercatchers to build a shortlist of agencies ahead of a pitch for the account.
Paul Weinberger, the agency’s partner, said: “The time has come for us to take control of our destiny and focus on building a strong, integrated and independent agency. As Tesco was our founding client and some of our people have worked with them for decades, this was a very difficult decision, but we are certain that it is the right one. We wish all the people at Tesco with whom we have worked so closely for so long all the very best.”