In what's described as an "oldies versus youngsters" battle, the membership - a powerful line-up of media, advertising and client bigwigs - is split over plans to update its constitution.
The most contentious proposal is one to allow women members. "It's what the older members get most heated about," one member said. "They refuse to countenance their admission."
The reformers are led by the current president, Mike Moran of Thames Water, and the president-elect, Douglas McArthur of the Radio Advertising Bureau. The traditionalists are being marshalled by Gordon Proctor, who was president of the club in 1973.
At a board meeting last month, a delegation of traditionalists mounted a rear-guard action against attempts at reform, in what one attendee described as "an outrageously heated debate".
The club, established in 1929, retains some of the most traditional trappings of the old gentlemen's club system. Of its 150-odd members, around 60 are core active members, while the rest are predominantly retired or not actively involved in the industry.
However, the club runs on a system of one member, one vote and reformers are worried that when the proposals are put to the vote in September the status quo will be fiercely defended.
"Without reform this club will eventually die because it has little appeal to the younger people in the industry and is old-fashioned and increasingly irrelevant," one member said.