Last week a 53 second clip, thought to be from the debut episode of the new series, was released unofficially online. The clip has since been removed by BBC Worldwide.
The BBC has confirmed it has requested a clerk at the California federal court issue a subpoena to Tapatalk, a mobile community platform in the United States, in order to get information allowing them to identify the source of the leak.
A spokesman for BBC Studios said
We take theft and illegal distribution of our content extremely seriously. We will strive to protect our programme-makers, audiences and licence fee payers from any breaches of security - ensuring Doctor Who fans enjoy the final and fully completed version of the episode when it premieresThe unfinished clip had temporary music and had not gone through the grading process which determines the final visual look of the scene.
Doctor Who has been plagued by leaks ever since it returned in 2005 when footage from Rose was released via a Canadian third party company. In that case the individual responsible for the leak had their employment terminated.
A leak 2013 was more embarrassing for the Corporation, when BBC Worldwide released the US Blu-Ray disc of the season climax before it had aired on television.
Doctor Who is due to return to screens this Autumn.