KS3 A wonderful opportunity to study British social history in the 1960s, Doctor Who demonstrates the early fascination with space travel and, therefore, time travel.
However, it is the concept of Doctor Who which has the most to offer history teachers. Ask students to imagine they are going to a particular period in time. All students can be enticed with this particular trick.
Would KS3 students rather be a peasant in 1300 or 1400? They would be better off in 1400, but only if they were one of the lucky ones who did not succumb to recurring bouts of plague. Another useful device is to ask students to compare different periods of history. The presence of usually malign aliens has definite Cold War overtones which might be of interest.
KS 4-5 Students at GCSE and A-level could use the Doctor Who concept (wonderfully illustrated by the Blackadder Back and Forth time travel episode) to consider counterfactual history, in which the significance of an event or individual is assessed by considering what might have happened if the event or individual had never existed.
Have a look at www.doc.ic.ac.ukaem3 ahhistory.html for some not terribly serious examples of this.