I've been writing Doctor Who fan fiction for fifteen years. My mother is certain the experience has warped me, making fourteen-year-old Canadian children like Peter and Rosemary speak like middle-aged Brits.
I suppose it's natural that, when branching off of Doctor Who fan fiction, one of the other genres I'd gravitate to would be Harry Potter. There are a number of similarities: both genres are British, and Doctor Who is, at its root, about a wizard (read 'Time Lord') who travels from adventure to adventure in a magic cabinet (read 'TARDIS'). Doctor Who pretends to be science-fiction and Harry Potter is middle-age fantasy, but I always thought the boundaries between science-fiction and fantasy were artificial and needlessly constricting.
But there are interesting differences. When I wrote The Grandfather Paradox, it was a standard time travel, meet-your-parents, avert-the-future type story that occurs often in science fiction, but in the Harry Potter setting, it was a fresh twist. Doctor Who is also a master of the isolated-base-in-peril adventure, something which hasn't yet been written about in Harry Potter fiction, but could be done to good effect. Doctor Who has done H.P. Lovecraft, but Harry Potter shows no signs of meeting any ancient gods. The central story of Harry Potter is about growing up and persevering in a very big and very scary adult world. Doctor Who has had many stories about facing life's challenges, but the hero has never had to come of age.
So, Harry Potter provides this author with a fertile ground of a new setting for old ideas, but also many challenges. Harry Potter just does not seem the right setting for an alien-invasion shoot-em-up. I've already seen the Borg invade Hogwarts, and they simply did not belong.