When does The Ipcress File return?

The Ipcress File is a British cold war spy thriller television series loosely based on the 1962 novel The IPCRESS File. Written by John Hodge and directed by James Watkins, it stars Joe Cole, Lucy Boynton and Tom Hollander. In 1963, spy chief Major Dalby gives small-time crook and black-marketeer Corporal Harry Palmer a way out of Colchester Military Prison by offering him a job as an intelligence officer in his small but influential Whitehall security unit, WOOC(P) The unit's investigation into a missing British nuclear scientist expands into a case of international espionage.
WOOC(P) is a (fictional) civilian department of the British intelligence community, reporting directly to the Cabinet. The unit's investigation into a missing British nuclear scientist expands into a case of international espionage which is documented in the eponymous "IPCRESS File"