What does the narrator imply by the 'popular island theory" regarding Magna Carta island?

That morning, the men arrive at Magna Charta Island, near Runnymede. As the name suggests, Magna Charta Island is where King John signed the Magna Carta in 1215. J. speculates at length about what it would have been like to be a peasant living in Runnymede at the time of the event.As the men approach Magna Charta Island, Jerome imagines what it would have been like to be a peasant when King John was forced to sign the Magna Carta in 1215. To a certain extent, this passage tips Jerome’s political hand. It is notable that despite his middle-class background (and his patronizing attitude toward ‘Arrys and ‘Arriets in the previous chapters), he identifies with the peasants rather than the bourgeoisie or the nobles. His positive description of the Magna Carta as “the great cornerstone in England’s temple of liberty” also hints at Jerome’s populist sentiments.