Grant by Hugh de Dunesden of his estates in St. Martin le Grand, London, with an important Jewish signatory from the Scaccarium Judaeorum, the Exchequer of the Jews at Westminster, in Latin, manuscript on vellum [London (St. Martin le Grand), first half of the thirteenth century (almost certainly within 1215-30)]

This is an important record of the influence of the English Jewry in the decades before the expulsion of 1290. In the witness list, alongside the London aldermen, Roger fitz Alan (who was sheriff of London in 1192-93, mayor in 1212, and appears frequently as a witness to charters of Westminster Abbey and St. Paul's), Robert de Wuberne (alderman in 1215-30, apparently of Aldersgate), the royal chaplain, Robert de Corneville and a significant London landowner, Salekin de Basing (who played a great role in the foundation of the Franciscan convent in London and donated land to Newgate Priory), occurs the name of "Josep Aaron" (here second line from bottom, second name from left).

Joseph Aaron is one of only two Jewish officials we can name from the Scaccarium Judaeorum, the Exchequer of the Jews – a subdivision of the Royal Court of Exchequer in Westminster, set up by King Richard I to keep records of debts owing to the Jews in England and to hear lawcases arising between Jews and Christians. The officers of this court had the status of barons of the Exchequer, subject to only the monarch, the treasurer and the chief justice. It is noteworthy that Joseph Aaron, who held office from at least 1198, appears as a witness here alongside senior city officials and a royal servant. It has long been suspected that St. Martin le Grand housed a section of the Exchequer, and this evidently included the Exchequer of the Jews with Joseph Aaron as a royal officer in permanent attendance.