What lit the fuse for this, was the release of a paperback edition of the LOTR books in the mid '60s that got people thinking about fantasy.
Miniature wargaming was expensive if you went into metal(then Lead), but luckily Airfix had a wide range of figures, for ancients to WWII, expanded by the Italian Atlantic company in the early '70s
These were small, 1/76 scale figures, that were close enough to use with the Airfix brand.
Britians company made traditional larger toy soldiers, but not in the range of Airfix. GHQ made WWII and modern 1/285 figures.
Tiny! Detailed!
Expensive!
What also hit in 1975 was Ral Partha miniatures showing new, highly detailed 25mm lead alloy figures, for wargames, with fantasy figures the nexd year. in '75 Grenadier also did Ancients thru the Old West in lead, not quite as nice as the Ral Parthas, but still great looking, compared to what Superior Miniatures had been doing.
by 1977, you had Citadel doing figures, mostly fantasy, as the D&D Juggernaut got rolling everyone started doing a fantasy line