The Chief Clerk (Prothonotary) and the Plea Side
From the clerkship of Robert Whitehill (c 1346 - c1373) at the latest, and very probably earlier, one clerk had greater responsibility and status than his fellows. Like the other clerks on the 'common pleas' or Plea Side, he acted as a filazer for a particular county or group of counties (notably Oxfordshire, suggesting perhaps an early connection with Shareshill, chief justice 1350-1361, although the connection moved to Kent in the late fifteenth century), and attracted private business as an attorney. Unlike the others, however, he had the monopoly of entering the records of appearance, through issue and pleadings, to judgment; in other words, he took responsibility for the formulation of the record at the point beyond which mere common form might not suffice.
At first it is not clear that this chief clerk was in authority over the filazers. He had a different function, but not necessarily a managerial role, except in relation to his own staff of underclerks. Gradually, however, as the primacy of his duties and his key role in the development of the court's business became apparent, so too did his role as the head of the Plea Side. The prothonotary's office, probably by design, was the chief beneficiary of the development of bill procedure, and the major steps in the use of the bill of Middlesex (the decision in 1452 that bail could count as custody, and from 1542 the use of the latitat as first process in a case) were reflected in enormous increases in the prothonotary's business, which from less than a third of Plea Side enrolments in the mid fifteenth century had swollen to well over ninety per cent by the mid seventeenth century, and to complete monopoly by 1702.
This expansion of business necessitated a steady increase in staff. When the post first emerges in the fourteenth century, a single chief clerk had one or more underclerks whose identities and duties cannot now be discerned; apparently ad hoc relationships with other filazers and attorneys; and perhaps a year or two of full association on the plea rolls with the person being groomed as successor. By c.1500 there was a distinct office with staff and perquisites, and sometimes a clearer sharing of duties between two men of virtually equal standing, although with only one formal postholder. By the end of the seventeeth century there were two full prothonotaries of King's Bench, with a secondary and a deputy, each with distinct duties and a team of underclerks.
The chief clerkship (the term 'prothonotary' was a fifteenth-century innovation) was not necessarily a matter of promotion from the ranks of the filazers; rather, it was commonly achieved by succession from within the office or firm of the incumbent, although appointment from elsewhere in the King's Bench secretariat was not unknown. By its nature the post was exceptionally lucrative; as well as the sorts of formal and unofficial fees available to a filazer both as filazer and as attorney, special fees for drawing pleadings and (by 1550) a share in fees for sealing judicial writs were reserved to the prothonotary. Substantial sums were paid (quite legitimately) to obtain succession to the office, and the holder was a person of great standing; John Roper (in office 1498-1524) married the daughter of the chief justice.