Let me be sure I name them correctly:
Bill Nighy played Rufus Scrimgeour in the Harry Potter films and has a appearance as Vincent van Gogh expert in the Doctor Who episode Vincent and the Doctor.
Shirley Henderson played Moaning Myrtle in the Harry Potter films and played Ursula Blake in the Doctor Who episode Love & Monsters. Do you remember? She had her face fused with a slab of pavement by The Doctor.
Zoë Wanamaker played Rolanda Hooch in the Harry Potter films, and the last living human named Lady Cassandra in several episodes of Doctor Who.
David Tennant played Barty Crouch Jr. in Harry Potter and the Goblet of Fire and the tenth Doctor.
Toby Jones voiced the character of Dobby the House elf in the Harry Potter films and played the Dream Lord in the Doctor Who episode Amy’s Choice.
Michael Gambon played Albus Dumbledore in the Harry Potter films and both Kazran & Elliot Sardick in the Doctor Who episode A Christmas Carol.
Helen McCrory played Narcissa Malfoy in the Harry Potter films, and a Saturnynian queen named Rosanna Calvierri in the Doctor Who epsiode The Vampires of Venice.
Additionally, not shown in the picture found on pinterest, John Cleese played Nearly Headless Nick in the Harry Potter films and has a small cameo in a Doctor Who episode titled City of Death.
