He sees in this some possibly uncomfortable realities about the past: "Few radical movements were genuinely intent on social 'levelling,' and even those figures who did advocate land reform ... largely did so with the dream of creasting a Britain of self-sufficient, independent smallholders. The urge remained at root individualist, or at best localist, rather than collectivist. This historical preference for a smaller rather than a bigger role for the state was scracely surprising, given that for most of British history the main business of government was to wage war, to raise funds to pay for it and to recruit men to fight for it."
He notes also another trend in British radicalism — a veneration of the law as the embodiment of liberties. Even where the law was seen as repressive, this was often seen as an innovation — at some past Utopia, often Anglo-Saxon times, it had done fufilled its "proper" role of protecting liberties. This, Vallance says, combined with another aspect of the radical tradition, its essentially patriotic outlook, leaves it open to Conservative cooption and even far right manipulation. The Levellers talked of the rights of the "freeborn Englishman" as the birthright of a particular nation.
So this is a history, but an intensely political, engaged with the present history. But it's not a polemic, and blessedly, it's highly readable and entertaining. Anyone who claims themselves a radical, or is heading perhaps in that direction, should read it, and have some idea of the successes — and failures — of those who came before.