The Time Lord's best friend…: The sonic screwdriver

Science fiction's most endearing and enduring gadget has to be Dr Who's sonic screwdriver. There was only ever one, and that was owned of course by the last of the Time Lords, and it was destroyed and recreated a few times. It has also evolved over the last 60 years - although what is evolving, and when, becomes indistinct when we are dealing with time travel!