I just got a copy of Matthew Raphael Johnson's book, Sobornosti: Essays on the Old Faith, which was recommended on another thread.
On page 122, in a list of innovations introduced by the Nikonians (polyphonic singing, western iconography, etc.) he also mentions "the banning of the Sarum rite (the Old Faith performed the Sarum rite on the feast of St. Gregory, from which the Synod of Milan takes its own Roman Rite)".
Does anyone know more about this? The Sarum rite under which form, and where?