She cried when she heard about a woman with terminal cancer who spent her last days on a sexual adventure – and knew she had to turn it into TV. As the devastating result hits the screen, the actor relives an extraordinary experience

‘I’ve done any and all number of sexual situations in my 30-year career,” says Michelle Williams, all matter-of-fact and puckishly charming. “But I’ve never masturbated on film before … and I was nervous. It’s much easier to portray mutual desire than just the desire for oneself. But God, when Liz [Meriwether] wrote those scenes – when Molly’s alone in the hotel and by the end she’s masturbating to anything, masturbating to a fish in a bowl! – I thought: ‘Oh Liz. You’ve really done it.’”

In Williams’s new show, Dying for Sex, she spends one entire episode masturbating – a staggeringly unusual thing for a woman to do on screen. Dying for Sex has a very simple premise, so grab-you-by-the-throat tragic that you’d almost take against it. Except it’s based on a true story, which was made into a podcast. Molly is 42, and in remission from a bout of cancer that has robbed her of the marital sex life that wasn’t all that anyway, when she gets the news that the cancer has come back, and is terminal. A palliative care nurse – brilliantly played by Esco Jouley – asks her about a bucket list. Her initial resistance gives way to the realisation that she’s never had an orgasm with another person, and that’s all she wants. So she leaves her husband to spend the rest of her short life chasing tail.