[Sticks]

Technically if you are recorded singing a song, you can be construed as violating two lots of copyright., The tune and the Lyrics. (They are treated separately in law)

C4/Endemol, in order to be consistant will have to ban whistling and humming as well, since that could be perceived as a violation of the copyright on the music.

The song they gave for Tim was not covered because the housemates composed the music as well as the lyrics, so the copyright belonged to C4/Endemol (Not the housemates)