The SFS organized the 1949 Eastercon and the 1951 International con in London, but collapsed shortly afterwards.

from Fancyclopedia 2 ca. 1959
Science Fantasy Society, sometimes with a prefixed English —-. It was organized just after the Whitcon by Ted Tubb, Ken Slater, VinĀ¢ Clarke, and a few others. It had an elaborate regional bureaucracy which amounted to nothing and a mailing system built around SF News, published by the Epicentre bhoys; the irregularity of the latter (the latter publication, clot) played hell with activity, and eventually Slater, who had been working Operation Fantast independently before the foundation of SFS, cut loose and set up on his own again. SFS ceased to exist shortly thereafter.