Susannah Fielding's Jennie Gresham has been the break-out star of This Time with Alan Partridge

This Time with Alan Partridge is a parody of the sort of cosy UK magazine programme epitomised by channel-mate The One Show. And that means Alan needs a co-host. So while Steve Coogan does his thing as the egotistical, yet quietly desperate, veteran broadcaster, Susannah Fielding is doing something arguably just as subtle in her spot next to him on the sofa, as fellow presenter Jennie Gresham.

Partridge fans knew Coogan had that multi-layered performance in his locker, but Fielding – who is perhaps best known for her theatre work – has been a revelation.

She based Jennie on all the "immaculate women out there on our screens – so Tess Daly, Holly Willoughby, Alex Jones obviously, Susanna Reid obviously. There’s a certain style that they all have... as soon as I got the script I thought ‘I know this world’”.

And her performance during the 'live' to-camera scenes is so spot-on – switched on in an instant, slick, upbeat, and with just a hint of the strain underneath it all – that it's easy to forget for a moment that she's not actually one of them.

When the smile drops and Jennie snaps back into business mode during the downtime between presenting segments, Fielding’s just as convincing.

She’s so good in fact, that once you remember that she is acting rather than actually hosting a magazine show, your eyes are often drawn away from Coogan to what she's doing – and as a huge Partridge fan, that is the highest honour I can bestow.

Perennial Partridge co-writers Neil and Rob Gibbons admit they didn't see the full potential in Jennie until Fielding auditioned for the role, but quickly realised she could add an extra layer of significance to the character.

“As soon as Susannah came on board – her audition absolutely blew us away, she totally knocked it out of the park,” says Neil. “She totally got it but she sort of suggested a hinterland to her character as well that wasn’t just someone who was an eye-roller and ‘oh god, why have I got to work with this guy?’, she had the sense of someone who was a bit of an operator as well, and as soon as we landed on that it gave us an in to have a bit more fun with the character.

“Originally, I think she probably would have been someone who was just a disapproving figure, and the audience see Alan through that character’s eyes, but when she starts nicking his jokes and trying to manipulate him with flirtation and things like that, suddenly you think ‘there’s a bit more in this, it’s a bit meatier than we first envisaged’.”

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Fielding says there are still lots of places for Jennie and Alan's dysfunctional relationship to go, and that there is an appetite among the team to do more This Time, although a second series is yet to be confirmed.

As things stand at the end of the first run, Alan is off to a meeting with the show's exec producer, the BBC Director-General and Jennie herself, presumably to discuss his position after inadvertently going on record claiming that she would “smother her own grandmother with a pillow to get on the cover of the Radio Times” (who wouldn't?).

The show can't go on without Alan, of course, but if the BBC want a second run as well observed and brilliantly entertaining as this one has been, they will make sure Jennie Gresham is back on the sofa next to him.

This Time with Alan Partridge is available to pre-order now, and will be in-store from 8th April