First she's part of Gangsta Granny (UKTV, Wednesday December 24, 7pm) starring alongside David Walliams in the adaptation of his best-selling children's novel.
The 2013 telefeature is about 11-year-old Ben whose parents (Walliams and Hart) want him to become a ballroom dancing star by entering him into a competition run by one Flavio Flavioli (singer Robbie Williams).
Things get worse for Ben when he is sent to stay with his unassuming granny (Julia McKenzie). He thinks that she is tedium personified, believing she is interested only in cabbage and Scrabble, but is delighted to discover that she is an international jewel thief.
He duly leaps on the back of her mobility scooter for one last heist: a raid on the Tower of London to nab the Crown Jewels.
Gangsta Granny.
Says McKenzie: "It may sound po-faced but the moral of this story is: don't underestimate people just because they're old. They have their own secrets, and they're not as boring as they might at first appear.
"I do think that we're a youth-obsessed culture. Of course I believe that because I'm old. But I still think it's true."
So one for grandparents and grandkids to watch together.
Hart is back as Chummy in the two-hour long Call the Midwife Christmas Special (One, 8.40pm, Boxing Day) which starts out with Vanessa Redgrave the show's narrator of the series, appears onscreen in 2005 as the late Jennifer Worth (the writer whose books which inspired the series) in 2005 before it flashes back to 1959.
There, while Christmas approaches Chummy is enlisted to help run a poorly managed mother and baby home, while Cynthia is drawn deeply into a case concerning two former residents of a Victorian mental hospital who have been left to fend for themselves.
A new season of Call the Midwife is due to air on One in 2015.
Also hot off the satellite from the UK will be the Doctor Who Christmas Special (Boxing Day 9am and 7.30pm).
Nick Frost stars as Santa Claus in the episode entitled Last Christmas, set at his North Pole Base where he, various elves, the Doctor and companion Clara come under attack from mysterious creatures.
The show is rumoured to be the one which will mark the departure of Clara (Jenna Coleman) from the long-running series and the episode features Michael Troughton, the son of 1960s Time Lord, Patrick Troughton.
And as for the techno paranoia one? That's the Black Mirror Christmas Special (Christmas Day, 8.30pm, SoHo), a 90-minute episode that follows the twisted Twilight Zone-like tales from Charlie Brooker's earlier two seasons.
Jon Hamm in White Christmas.
The one-off, entitled White Christmas stars Mad Men's John Hamm as a digital entrepreneur.
One of the three story strands involves what would happen, says Brooker, if we gained the ability to block people in real life as we do on social media.
Just the thing to see off all that festive season bonhomie with, then.
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