The great Victorian historian of the civil war, S. R. Gardiner, described the Protestation as ‘the Tennis Court Oath of the Puritan Revolution’. Long after the Restoration, subscription to this pledge to defend the ‘true reformed religion’ was seen as a clear indicator of Parliamentarian sympathies: Mark Noble's 1798 collective biography of the English regicides assured its readers that every one of them had taken the Protestation.

John Walter's new book, the first monograph-length study of the Protestation, follows these earlier assessments in laying bare the radical intent of what effectively became a Parliamentarian oath of loyalty. Walter begins with a forensic examination of the Parliamentary history of the Protestation, clearly demonstrating that an earlier draft of the test contained a more conditional promise of allegiance to the Crown. Exploring these variant texts is important, as Walter clearly shows, not only for demonstrating the political motivations of its framers, but also because the draft text circulated in print. Walter argues that the printed copy of this version of the text, the ‘City Orders’ as he terms them, was employed to direct subscription to the oath in London and other parts of England.

As Walter then makes clear, the architects of the Protestation in Westminster were not acting in isolation but in coordination with supporters in the City such as John Venn and Cornelius Burges. It was these supporters who were behind a petition of 3 May 1641 which alerted Parliament to Royalist plotting, giving renewed urgency to the debate over the Protestation. In requesting that the citizens of London also be allowed to subscribe to the Protestation, these allies outside of Parliament were also preempting the use of the oath to mobilise public support for the Parliamentarian cause. Pressure from outside of Parliament, Walter shows, was also deployed to recover some of the original intent of the Protestation: scruples over subscription in the City were used as the pretext for the addition of an explanation to the text which made clear that it did not require those taking it to maintain ‘any form of worship, discipline, or government nor of any rite or ceremonies of the Church of England’. It would be the same combination of the Parliamentary leadership with its City supporters which would finally secure the order for nationwide subscription to the Protestation in 1642.

The Protestation was now part of a national conversation conducted through manuscript letters and treatises, as well as printed sermons and pamphlets. For some godly ministers, such as the Presbyterian John Geree, the Protestation was England's National Covenant to defend the country from the threat of popery. As Walter notes, the obligations placed on subscribers by this English covenant were not purely spiritual, the arguments of Puritan preachers offering a ‘powerful stimulus to the development of a popular parliamentarianism’ (p. 91). Some divines took these arguments further: Henry Burton's Protestation protested (1641) reinterpreted it as a manifesto for ‘radical religious reformation’ (p. 94) and the replacement of the national Church with independent congregations. In response to the Parliamentarian glosses of ministers such as Geree and Thomas Mocket, casuistic literature emerged, parsing the ambiguous language of the Protestation to provide a reading that could be accommodated with Royalist sympathies. Some ministers would later subscribe to the Protestation with exceptions or equivocations along these lines. These readings, Walter observes, none the less assumed that the Protestation was being employed to mobilise the nation against the king's party. By 1642 this was clearly the case as writers such as Henry Parker and John Goodwin stressed that the oath obliged subscribers to defend Parliament.

The next two chapters of Covenanting citizens consider how this mass mobilisation of the public was achieved through an analysis of first the administration of the Protestation and then an exploration of the process of securing subscriptions. Walter finds that subscription to the Protestation was not limited to a few City parishes in 1641 but that, instead, Parliament successfully exploited national networks of the godly to ensure that many English boroughs had already taken the oath before nationwide subscription was ordered in January 1642. Walter has also found at least some evidence of subscription to the Protestation in three-quarters of English counties in 1641. Sites of early subscription to the Protestation, Walter suggests, can ‘provide a litmus test for the detection of proto-parliamentarian activism in the country’ (p. 137). Equally, areas where records of subscription to the Protestation are lacking, such as in the counties bordering Wales, point to opposing areas of Royalist strength. (A minor criticism: it would have been helpful here if Walter's analysis of the geography of subscription and non-subscription could have been supported with maps.)

The act of subscribing to the Protestation was also heavily infused with political and religious meaning: it was no coincidence that several parishes chose to take an oath to preserve the Church from the forces of popery on 5 November. Foreshadowing the sermonising that would accompany the later Parliamentarian oath, the Solemn League and Covenant, other parishes followed the ‘City Orders’ in having the minister deliver a sermon explaining the obligations of the Protestation before subscription. As Walter's final chapter demonstrates, this proselytising effort did not fall on deaf ears: the Protestation was seen as authorising other forms of subscriptional activity, notably popular petitioning in support of Parliament; for others, it legitimated direct action, with subscription to the Protestation a trigger for iconoclastic attacks across the country; and for some, it was a new ‘oath of association’, like its Elizabethan predecessor, calling its subscribers to arms.

In Covenanting citizens, Walter convincingly argues that the Protestation was critical to Parliament's efforts to mobilise the nation. In so doing, Walter makes a significant contribution both to the historiography of the outbreak of the English Civil War and to the burgeoning historiography of ‘subscriptional texts’ (as Mark Knights has described oaths, petitions and addresses). While Walter acknowledges that the Protestation could be read as offering ‘a set of political commonplaces’ (p. 81), he also successfully demonstrates that Noble and Gardiner were right to identify it as a revolutionary ‘Shibboleth’.