Because I have this notion that someone might read this who doesn’t regularly visit the DWAITAS board, I thought I’d repost my response to this query:
"Got three adventures ready for my players: Two in Earth's past and one on a distant planet, but feel that I'm missing something for present-day Earth. Any ideas?"
Modern-day adventures often relate to modern-day PCs, acting as origin stories or jumping-off points, or grounding them with families and friends, so if you have no modern-day PCs they become less relevant. (That said, visitors from other parts of time and space will always have an interesting perspective on the present.)
They can also be fairly low-key, which can be harder to think up - although they don’t have to be, as seemingly world-changing events like first contact or Dalek invasions can still be shrugged off by the general populace or individual characters.
And they aren't necessary either - look how little time the Eleventh Doctor has spent in the present, just enough to pick Amy and Rory up and drop them off again, give or take an adventure set ten years ago or ten years ahead.
Personally, though, I like the juxtaposition of fantastical elements with the everyday world. Aliens marching around are more surprising in a service station than a space station. And you can play with modern concerns - The Sontaran Stratagem looks at pollution, global warming, space colonisation, and the thought most of us have had when using satnav, “what if it’s wrong?” exaggerated to “what if it’s lying?”
And if you’re really stumped, you can always use something very Doctor Who specific like being called in by UNIT, or adapt from a modern-ish horror game like Call Of Cthulhu.