It was based on the idea that there was something wrong or illegal to hold left wing views, as was the Cold War
In fact, that has never been the case in Britain - yet
The left didn't "infiltrate" the revival, as suggested, but were a major part of setting it up -
The promotion of the People's Music always dominated their efforts - Alan Bush, Gerry Sharp, Bill Leader, Dallas, MacColl, Lloyd et al - even Sharp in the early days, who was a Fabian Socialist of the post- Victorian, Edwardian type
The right attempted to make fols song anodyne and harmless - songs sung by 'The Salt of the Earth' or 'The Sons of the Soil'
Jim Carroll