[Spoilers] Sir Harry Pearce

[Silktie]

You're right, one of the producers said in one of the commentaries that Harry was initially meant to be a secondary character, but that once the writers saw the way PF porttrayed him, they loved writing the character and just kept on putting in more and more scenes for him. I think that's evident in season 1, where he was peripheral in the first two episodes in particular, but gradually grew in importance from 1.3 onwards.