“Daughter, wife, mother. There are my roles. I chose them, for better, for worse. And then you came along and exploded all of that.” So went Julia Ormond’s scene-setting monologue on Gold Digger (BBC One) – a psychosexual thriller about an age-gap romance with possible ulterior motives.

The BBC are hoping this six-parter, written by Marnie Dickens, will keep audiences glued to their sofas on autumnal nights and get tongues wagging around watercoolers. With its saucy intrigue and chic interiors, it was bidding to be an upmarket melodramain the mould of Apple Tree Yard or Doctor Foster.

We began with Julia Day (Ormond) waking up alone in an enviable Devon pile on her 60th birthday – the first since her husband of 35 years, Ted (Alex Jennings), left her for her best friend. She headed to London to celebrate with her three grown-up children but one-by-one, they blew her out. Grrr, those pesky kids.

Left at a loose end, Julia tossed her impressive curls, donned her swishiest green coat and wandered into the British Museum – where a chance encounter with flirty thirtysomething Benjamin (Ben Barnes) proved to be the beginning of a whirlwind affair.

All that was left to do was introduce him to her children and that’s where things became fraught, not least because the entitled brats initially mistook him for a waiter. They immediately presumed that suave young stud Benjamin was only after one thing – her money (“Mum has the house, the villa, the investments”) – so started plotting how to remove him.

There were hints of trauma in the Day family’s past, possibly involving violent abuse, so expect dark secrets to bubble to the surface. Besides, Alex Jennings is too good an actor to be wasted in a cameo role as a midlife crisis cad. Anyone who saw him play a serial killer in last year’s ITV drama Unforgotten knows how chilling he can be.

Invariably the norm on-screen is older men with younger women, so redressing the balance was welcome. It was refreshing to see an older woman taking risks, being recognised as a sexual being and feeling “seen” for the first time in decades.

Such a set-up might have been smartly compelling and precision-tooled to get viewers talking at home but sadly, the story’s execution was overwrought and soapy. Dialogue was stagey and stilted. Ormond aside, the cast didn’t convince. The tidy-bearded toy boy was smug rather than charming, while her irritatingly self-absorbed children needed a stern talking-to.

Only over-protective eldest son Patrick (Sebastian Armesto), a stressed City lawyer with his own dysfunctional marriage but determined to atone for the sins of his father, was remotely three-dimensional. He was left to do all the heavy lifting on behalf of his two sketchily drawn siblings, spoilt slacker Leo (Archie Renaux) and heartbroken lesbian Della (Jemima Rooper). That is, when Patrick wasn’t pouting sulkily, randomly punching walls or getting into moody staring contests with Benjamin.