Modern master of the melodrama Todd Haynes (Carol, Far From Heaven) turns a tabloid scandal into an A-list Lifetime movie in this fascinating and sometimes very funny face-off between two female performers at the top of their game. May December follows a famous actress as she shadows, mimics and snoops into the secrets of a woman she’s set to play on film.

Natalie Portman plays Hollywood star Elizabeth, with Julianne Moore her subject Gracie, a housewife and not particularly successful baker who hit headlines two decades previously and has also spent time in jail. Hoping to win favour but risking everything in the process, Gracie lets Elizabeth into the life she shares with her children, and much younger husband Joe (Charles Melton). Screenwriter Samy Burch (who conceived the story with Alex Mechanik) drip-feeds us the salacious backstory, loosely based on that of Mary Kay Letourneau.

Playing a self-important and manipulative actress who knows the power she possesses and isn’t afraid to stir up trouble for the sake of art, Portman sends herself up, and indeed the whole acting profession, while Moore makes for a mesmerising, spiky and unpredictable foe. It all proves totally irresistible as Elizabeth turns detective and seems to set her sights on the wide-eyed and awkward Joe, while an elegant yet overblown score camps things up immeasurably (composer Marcelo Zarvos has adapted Michel Legrand’s seminal work on 1971’s The Go-Between). Our heroine is supposed to be hunting for humanity but she is, let’s be honest, only really digging for dirt.

May December screens at Southbank Centre, Saturday 7 October, and BFI Southbank, Wednesday 11 October as part of the BFI London Film Festival; in cinemas from Friday 17 November, and on Sky Cinema and NOW from Friday 1 December.