Line of Duty star Keeley Hawes has been cast as the villain in the new series of Doctor Who, to screen later this year on BBC1. She will play Ms Delphox, a villainous banker with a dark secret. It's another impressive feat from casting director Andy Pryor, and proof that the biggest names will still jump at travelling to Cardiff and doing lots of silly work with green screen.

Hawes said of the news: "I am delighted to join Doctor Who and to be working with this incredible team. Ms Delphox is a great character and someone I've had a lot of fun playing."

The show's current creative engine Steven Moffat adds: "Anyone watching Jed Mercurio's amazing Line of Duty will know that Keely Hawes is having one hell of a year. And now it's about to get even better as she achieves the greatest villainy yet attempted on Doctor Who: she plays a banker."

This is nothing but good and exciting news, and here is why.

She's the woman of the moment

Hawes has long been one of the leading lights of TV drama's loose repertory company. But her turn in Line of Duty has proven to be her finest hour. As the icily malevolent DI Lindsey Denton, a cop under investigation for corruption who may or may not be guilty of crimes even worse than the ones she's being investigated for, she's already a shoo-in for next year's awards season. The show, and Denton, has broken further ground in the portrayal of women in the force. And Hawes owns it, electrifying the screen precisely because she does it so downplayed and dowdy; her complex character has been mentioned in the same breath as The Killing's Sarah Lund.

She's already pretty much cult royalty

Here is a woman who has served enough time on the nerd benches, or rather, the greatest UK genre shows in recent memory. She was one of the original Spooks, playing case officer Zoe Reynolds for the first three series, and then managed the unthinkable. When John Simm brought timeslipping crime drama Life On Mars to an abrupt end by quitting, not many people thought it was a great idea to work up a sequel set in the 80s. But as Alex Drake, a cop caught in a similar time-shifted quandary, she made the show the equal of its predecessor, repurposing the format from butch Sweeney homage to a deranged riff on Moonlighting with extra shoulderpads and speedboats.

She'll get to camp it up

Whether toting guns as Alex Drake or preening about as Lady Agnes in Upstairs Downstairs, Hawes always carries herself with a steely presence. She has that TV actor skill of gripping tight on your attention in close shots and small rooms. But she's never really had the chance to properly let loose. Doctor Who villains are a unique bunch: never straightforward evil geniuses, but complex characters able to let it all hang out by virtue of being in a show about space badgers and such. Moreover, Hawes is playing a banker, the most consensually villainous occupation in the modern world. Political subtext and a frightwig? We're excited about this character already.

Insane fan theorising can begin all over again

Hawes has been announced as playing a banker called Ms Delphox. But when did we ever allow what we were told to get in the way of what we decide we want to happen? The traditional response to the announcement of a female adversary leads the forums to wildly speculate: "Could she really be the Rani?" as if bringing back a twice-used 80s panto villain played by Kate O'Mara would be high up Steven Moffat's to-do list. So let's go one further. Sylvester McCoy apparently let slip recently that supervillain the Master was returning this year. Steve John Shepherd has emerged as the rumour-mill's favourite to take the role, but consider this: the fuss over Peter Capaldi's casting led it to being laid down in canon that, yes, a Timelord could change gender. Could we, in fact, be looking at Hawes as our first female Master?! And away you go ...