It contains about 50 large illustrations of a very high quality that have no equivalent in English books. Because of this lack of comparison, specialists must seek information in the details of its content.
Dating it in the first twenty years of the sixteenth century seems incontestable. At that time the illuminations reached an unprecedented quality in Flanders, in a leap forward facing the progress of the printed books.
The book was made for a member of the Tudor court. It shows as a saint the late King Henry VI for whom Henry VII Tudor was unsuccessfully trying to obtain a canonization. The dedicatee and his family are shown on many images. The hypothesis that he could be the future King Henry VIII was considered in the nineteenth century.
Above all, the pre-eminent place among the saints is granted to St. Roch, invoked against the plague. In 1499 and 1500 this disease infects London and King Henry VII finds a temporary shelter in Calais. The plague then spared London until 1537, which was much too late for the pictorial techniques used in this manuscript.
Another saint listed in this book of hours is the Welsh Armel who entered the calendar in 1498. The Tudor family was partly of Welsh origin.
In the absence of other significant elements the date of 1500 may be accepted. If the reference to St Roch is a thank and not a call, the work may however be slightly later. As far as I know the identification of the workshop has not been discussed. I think that a Flemish origin should not be dismissed, to be correlated with the temporary exile of the king.