In the "classic" series, most stories seem to have a unique musical score that aws not repeated in later adventures. There were a few exceptions, of course. Adric's "theme" from "Full Circle" was used again in "EarthShock". But for the most part, each story had its own arrangement.
In contrast, the "new" series (2005 and onwards) wound up creating distinctive "signature" themes for many of the continuing characters or "recurring" monsters. Obviously, the Doctor was given a "signature" theme. I heard somewhere it was called "Flavia's Lament", but that's probably just hearsay or an early "working title".
A very interesting and "lamentful" score, clearly suggesting the Doctor's loneliness, but I must wonder why the PTB didn't use elements of the Ron Grainer theme. For anyone who has seen Tom Baker's debut story, "Robot", remember the scene when the Doctor emerges from the TARDIS several times sporting a different ensemble? You know, the clown, the viking, and the Tudor style royal robes... When he finally exits the box sporting his iconic fedora and scarf, we hear the first three notes of the Derbyshire arrangement. It suggested, at least to me, an element of "mystery". It also helped to signify "This is it; this is the Doctor".
I have no real complaints, but I think it would've been neat to "weave" elements of Grainer's score into the Doctor's "signature" theme. Imagine the scene in "School Reunion" when Sarah discovers the TARDIS and then whirls around to see "Mr. Smith", finally realizing who he really is. Those three opening notes would have been perfect!
What are your thougts?