in the u.k they are advertising the game--harry potter and the chamber
of secrets on t.v. what is the music that is used in the t.v ad? who
is it by? and what is it called?

I haven't actually heard the ad, but I would be very suprised if they
weren't using the music from the actual games.   This music was
composed by Jeremy Soule the renowned game composer
(http://www.jeremysoule.com) and performed by the London Philharmonia.

This music was made and composed by Jeremy Soule the renowned game composer
(http://www.jeremysoule.com) and performed by the London Philharmonia.