Torchwood

This idea, originally titled Excalibur, was abandoned until 2005, when BBC Three Controller Stuart Murphy invited Davies to develop an after-watershed science fiction series for the channel.

During the production of the 2005 series of Doctor Who, the word "Torchwood", an anagram of "Doctor Who", had been used as a title ruse for the series while filming its first few episodes to ensure they were not intercepted.

Davies connected the word "Torchwood" to his earlier Excalibur idea and decided to make the series a Doctor Who spin-off.

Subsequently, the word "Torchwood" was seeded in Doctor Who episodes and other media that aired in 2005 and 2006.

Because Torchwood is shown after the watershed – that is, after 9 pm – it has more mature content than Doctor Who.

But it's the essential difference between BBC One at 7 pm, and BBC Three at, say, 9 pm.