I was listening to a radio interview with Lesley Sharp, and idly wondering (as you do) if she had ever done any Big Finish (not yet), when the interview went on to how excellent she’d been in the Tenth Doctor story Midnight.
It then moved on to mention that Russell T Davies had considered Lesley in the role of the Doctor! I did a bit of digging and found an article from 2008, nine years before Jodie Whittaker would get the part.

In the article (Writer Russell T Davies backs Lesley Sharp to be first female Doctor Who) RTD suggests that had he stayed, he would have cast Lesley Sharp (or perhaps Catherine Zeta Jones) as the Eleventh Doctor instead of Matt Smith! Just imagine what might have been…