Since the departure of Donna, the TARDIS has been lacking in silliness. Not that its a vital component but it certainly added a few laughs to the episodes each week. Personally, I see Barbara as being a similar character. Miranda Hart is one of those comedians who can be likened to Marmite, but her appearance in Not Going Out is definitely hilarious. Shes already an assistant, both in the amount of air-time she gets and in her job as a cleaner, so it wouldnt take much for her to adapt to the role of companion. All the while, shed offer clever and funny insights to the goings on in the universe. Much like Donna, Barbara isnt the cliché young, pretty assistant that will probably fancy the Doctor, so it would be once again refreshing to see the Doctor travelling with a friend who makes him laugh.