So what do we think of Miranda Hart's performance so far in Call the Midwife?
Or, rather, what do we think of Miranda's entrée into the world of straight acting, in what some critics keep referring to as BBC1's "surprise hit" (ie the sort of programme they would not normally watch)?
Personally, I have found it quite hard to judge, because Hart's character, Chummy, almost amounts to a case of typecasting as she accidentally upsets a hospital trolley, learns to ride a bicycle, and so forth. In fact, when I interviewed Hart just before Christmas, she worried that this bordering-on-slapstick stuff wasn't removed enough from her BBC1 comedy. "Where she knocks over something I slightly cringe," she told me. "Viewers might be expecting me to go for a quick laugh."
What this viewer has kept expecting Hart to do is to have a quick look at the camera, in the same way her comic alter-ego mugs in Miranda. As it happened, Hart/Chummy's eyes do seem a bit restless, perhaps with the effort of finding somewhere else to rest. And then she kept baring her teeth in an Upper Class Twit of the Year fashion. But if Miranda is learning how to ride the bicycle of straight drama, then she has got herself on a runaway two-wheeler. Call the Midwife's ratings (nine million and rising – almost Downton numbers) meant it earned a recommission after just two episodes.
The temptation for comedians to branch out into straight drama is a strong one. It's a chance to prove that they are more than a one-trick pony, while drama commissions are rather thicker on the ground than comedy ones. Perhaps it's why they got into comedy in the first place – with half an eye on the acting fast track. And don't all jokers, from Charlie Chaplin and Buster Keaton onwards, want to show that they have a serious side? Hell, even Jerry Lewis – more of a cartoon than a human being – became the straight man in Martin Scorsese's The King of Comedy. His co-star, Robert De Niro, has of course since travelled in the opposite direction.
The more eclectic the personality, the more likely they are to break into straight. Robin Williams has been shedding his comic persona since Dead Poets Society in 1989, but it wasn't until Christopher Nolan's Insomnia in 2002 that he finally managed to rid himself of the need to be liked. Eddie Izzard could probably take up painting or politics or poetry without pausing for breath, but his appearance in a Second World War German general's uniform in Valkyrie might have surprised people used to him wearing a skirt. Is he any good? I thought that his Long John Silver in Sky1's Treasure Island was left rather exposed by mixing with the likes of Donald Sutherland and Elijah Wood. I reckoned the same of Steve Martin in Lawrence Kasdan's 1991 ensemble drama, Grand Canyon, although Martin's great chum, Billy Connolly, did a sterling job reining in his natural exuberance in Mrs Brown.
But then a certain broadness is to be expected. It's perhaps why producers of Dickens adaptations favour them: Catherine Tate, Alistair McGowan and Johnny Vegas in BBC1's Bleak House, and Dawn French and Paul Whitehouse in their David Copperfield. The same goes for ITV1's Miss Marple whodunits – hammy affairs that easily incorporate the likes of Harry Enfield, Jessica Hynes and Alexei Sayle.
And then there are the graduates of Cambridge University Footlights, most notably Emma Thompson and Hugh Laurie, who have seemingly had no problem moving into straight acting – something which might not be entirely disconnected to the supreme self-confidence fostered by that establishment. And the future for Miranda Hart? You've got to be kidding. Between them, Miranda and Call the Midwife will have Hart's diary stitched up for the foreseeable.