I think it was the Spanish Civil War which caused major debate and controversy within the SPGB over its "sole objective."

A hard core doctrinaire group within the SPGB always opposed any, every and all other demands as "reforms" and distractions from the "sole objective of socialism."

The more open majority within the SPGB (and still is) reasoned that as they advocated the establishment of socialism through democratic parliamentary means (that is a whole other debate), you had to first have democracy and a parliamentary system in order to be able to use it to establish socialism. Given that those fighting to defend the democratic Spanish Republic were indeed fighting for basic democratic rights and a democratic system of government they perhaps should be supported in that endeavour.

The hard liners of course vigorously opposed this but never answered the question of what the role of the SPGB should be in the absence of parliamentary democracy. Hibernate probably.

Some of this was reflected in the SPGB statement on the opening of World War Two when it supported all those fighting against the Nazi and Fascist dictatorships (anathema to the hard liners) and in the splits in the late 80s and 90s which included the breakaway SPGB, the Ashbourne Court Group.

Marxism-Leninism (another anathema to the SPGB) of course advocates revolution to establish socialism and in the absence of democratic rights and a system of democracy to fight for such, alongside working class democracy and socialism itself. We have never had any problem fighting for more than one demand at a time!