Since then Blair Worden has ranged much further afield, with a major study of the literature and politics of the Elizabethan period, and a book about later interpretations of the "Roundhead" radicals that traverses the 18th and 19th centuries. But he has always remained the pre-eminent historian of the politics of the Interregnum, and every essay or article that he has published in that field has become a landmark study for those who work there. His new book is a collection of such pieces. Two appear here for the first time, and several of the others have been revised and enlarged. The resulting volume will of course be indispensable for fellow specialists; but it also offers a fine introduction, for the general reader, to some of the best modern historical thinking on the political and mental worlds of the Cromwellian era.

That Oliver Cromwell is the dominating presence here is to be expected. What is important is that he dominates, so to speak, on his own terms. Two of the pieces Worden reprints are classic essays in which he reclaimed Cromwell from the Whig tradition by restoring his religious and providentialist mindset. Here was a politician for whom the most demanding test of any decision was not whether it embodied a political principle or gained an advantage, but whether it furthered the working out of God's will. Similarly, in another essay, Worden disentangles Cromwell's concern for "liberty of conscience" from the modern principle of religious toleration. "The goal of liberty of conscience was very different from that of modern liberalism. It was religious union, which persecution was held to have destroyed: the union of the believer with Christ, and the union of believers with each other."

However, while Oliver Cromwell's mental world was far removed from that of modern liberal politicians or theorists, he could not have survived politically if he had not possessed some of the skills that modern political leaders also need: the ability to adapt to events, and the capacity to appeal to people outside one's own ideological group. Cromwell's political pragmatism may have been grounded on the belief that such tactics would best serve God's overall purpose; but pragmatic, in effect, it certainly was. In one rather delicious passage, Worden comments on Cromwell's extraordinary "feats of ignorance": he managed to be away from London until just after Pride's "Purge" of parliament had taken place in December 1648, and when the so-called Barebones Parliament was terminated by an army coup in 1653 he contrived to know nothing about it. (This is a rare skill, though one that particularly inheres, it seems, in Members of Parliament for Huntingdon: in 1990 Cromwell's feat was matched by his successor John Major, who remained incommunicado, following a dental operation, at the crucial moment when support was sought for Mrs Thatcher's survival as prime minister.)

The longest essay in the book is on how the Cromwellian regime affected life and politics in the University of Oxford. This is not the donnishly inward-looking topic that it may at first sight appear to be. England had only two universities, and most of the country's clergy and intellectuals were trained there: control of these institutions was vital for long-term regime stability. Worden's account — greatly enlarged here — is important not just for that reason, but also because it offers such a thorough case-study of how practical compromises were made, as Cromwell encouraged or permitted the development of a modus vivendi with people who disagreed with him on fundamental issues. It is also a superb example of what it is now fashionable to call "thick description", with telling details culled from an astonishing range of archival sources.

But this book is not just about Cromwell and his beliefs or policies. Several of the essays chart larger shifts in political thinking in this whole period. How did people come to assume that "civil and religious liberty" was one liberty, or at least two necessarily conjoined, when their thoroughly pre-Whiggish assumptions did not supply any reason for automatically putting the two together? Step by step, Worden traces this important mutation in popular political thinking, demonstrating on the way the somewhat opportunistic role played in the story by Cromwell himself. And when did people — that is, any broad part of the spectrum, as opposed to extremists and oddballs — come to think that England should be a republic, dispensing with kingly rule? The answer here is even more surprising: republicanism (if one may use that term) did not lead to, but followed, the execution of the king.