Early trail for The Witch's Familiar

Viewers to BBC Two this morning had a surprise when the channel transmitted a trailer for the second episode in this year's series, The Witch's Familiar, some twelve hours before the first episode is broadcast.

The trailer went out at 7.25am, just after a screening of the 1934 film Anne of Green Gables, and contained spoilers from episode one.

This is not the first instance of the BBC releasing information too early. In 2013 the Blu-Ray version of The Name of the Doctor was distributed in the US before transmission of the episode, while in 1983 the Target novelisation of the twentieth anniversary story The Five Doctors, was available up to two weeks before transmission.