Originally uploaded by Aristibule.
The Sarum Cassock is not clear in this case. However, one can see the wide sleeves of the Surplice which is variously called Old English, Medieval, or Warham Guild style. It is thought by some to be a type of alb, possibly from the old Gallican Alb of the early Western church (an unbelted voluminous white linen garment) - a more abbreviated form is variously called Anglican or Benedictine, and the extremely abbreviated form with lace is the Roman style (with a square yoke, and extreme abbreviation, one has the Cotta .. a similar garment.)
This is what a priest would wear praying the Divine Office or Hours (Morningsong, Evensong - Matins, Lauds, Prime, Vespers, Compline, etc.)