The story by Mark Gatiss will air in the UK on 17th April. The time is provisionally set as 6.20pm - 7.25pm, although there has been no indication that the episode is any longer than the usual 45 minutes. The extra time listed probably belongs to Casualty which is currently listed as 30 minutes long. Final schedules will be released next Wednesday.
The Doctor has been summoned by an old friend, but in the Cabinet War Rooms far below the streets of blitz-torn London, it's his oldest enemy he finds waiting for him, as the time-travelling adventures continue. The Daleks are back – but can Winston Churchill be in league with them?