It is now estimated £ 850K for sale by Christie's in London on July 13, lot 113. The date of the Millon sale in Christie's catalogue departs of one year from the real date. The story below is mostly based on my 2012 discussion with some additional information concerning the artists.
Note also that this beautiful manuscript was not complete as eight of the twelve calendar pages and three folios that probably supported large miniatures are missing.
The atmosphere is weird in Paris after the death of Charles VI in 1422. The new king of France is the infant Henry VI of England who of course does not reside in that city, and the regency is entrusted to his uncle the Duke of Bedford.
Throughout Europe the princes are competing in luxury and commission to the most skilled artists the illuminated books, the great art of that time gloriously promoted by the duc de Berry who had died in 1416.
From 1409 to the 1430s, the leading (and probably unique at some time) Parisian illumination workshop is led the Master of the Bedford Hours so called by reference to his main patron..
The manuscript for sale is a book of hours in Latin and French for the use of Paris. It consists of 265 vellum folios 22 x 16 cm, mostly in-octavo. Its illustrations include but are not limited to 22 nearly full page arch topped paintings in three side frames. The text is carefully line ended and ruled.
The sumptuous models by the Bedford Master had been transmitted to his joint successors whose hand is recognizable in the manuscript for sale : they are the Dunois Master and the Master of the Munich Golden Legend. Such attributions enable to date that work from around 1440.