Found-- this intriguing bookplate. It can be seen in many books deaccessioned from the club's library. Until I researched the Forum Club I thought it had some occult or theosophical connection, as the women look like priestesses witnessing some sort of vision or apparition. In fact it was a normal London club, but solely for women, with 1,600 members.
It was founded in 1919 as The London Centre for Women's Institute Members, and lasted into the early 1950s. A number of suffragettes and early feminists were members, including Elizabeth Robins, Mary Sophia Allen and Sybil Thomas and Viscountess Rhondda. As well as accommodation for members (and their maids), the club contained a dining room, a lounge, a photographic darkroom, a salon which could by hired for exhibitions, a bridge room, a billiard room, a library and a hairdresing room. Formerly it had been the residence of of Sir Henry Campbell-Bannerman, who was Prime Minister from 1905 to 1908. A blue plaque commemorates his residency. During World War I it was The Princess Christian's Hospital for Officers - a convalescent home with 35 beds, affiliated to Queen Alexandra's Military Hospital in Millbank. A website in 2012 reported it was now boarded up but it will probably re-emerge as an oligarch's palace or a hotel.