Close-up: Jessie Cave

Why Harry Potter's new friend decided to swap centre court for centre stage

Playing a young girl gifted beyond her years might be less a stretch for Jessie Cave than for most. Admittedly, unlike Thomasina, her character in Tom Stoppard's Arcadia, currently enjoying excellent reviews in the West End, Cave has yet to propose a startling new theory of chaos mathematics. But at just 21, she has some impressive achievements under her belt. Besides her role in David Leveaux's Stoppard revival, Cave will hit cinema screens around the world this summer as Lavender Brown in Harry Potter and the Half-Blood Prince.

With two such coveted gigs on her CV, one might assume Cave to be another stage-school kid, but the Londoner actually landed the Potter part at an open audition, and, until Arcadia, her stage experience was limited to school plays. "It's taken me a while to find my purpose," muses Cave. Indeed, besides an art-foundation degree and an aborted stint studying English at university, she nearly became a pro tennis player: "I'd have had to give up my life just to be in the top 500 and I didn't have that love for it."

But her passion for acting is manifest as she gushes about Stoppard ("So sweet how he lines up his gummy bears and cigarettes on his desk!") and shrugs off stage fright ("I blanked my lines in rehearsal, but it's all about getting back on the horse.")

So, are we likely to see Cave in the front-row of fashion shows like fellow Harry Potter star Emma Watson? She isn't sure, but in the meantime she has other passions to keep her occupied – a part-time degree in illustration and collecting vintage buttons. How appropriately wholesome for such an English rose.

'Arcadia': Duke of Yorks, London WC2 (www.londontheatre direct.com), until 12 September