When does All Creatures Great and Small return?

All Creatures Great and Small is a British television series made by the BBC and based on the books of the British veterinary surgeon Alf Wight, who wrote under the pseudonym James Herriot. Set in the Yorkshire Dales and beginning in the mid-1930s, it stars Christopher Timothy as Herriot, Robert Hardy as Siegfried Farnon, the proprietor of the Skeldale House surgery. The supporting cast, both recurring and one-off, numbers over 600, most of whom appear as farmers or clients of the surgery.