The Favour and Let’s Pretend are set in glamorous places exclusive to the ultra-wealthy. How did you research their glossy lifestyles?

I cheated a little with my research for "The Favour" as it has some decidedly autobiographical elements - like Ada, I went on an art history gap year course in Italy, where I felt as if I was only person on the course who didn’t have the charm, wealth and confidence of a public school education. Revisiting my God-awful teenage diaries from the time was excruciating. On the other hand, reading Tatler for tips on posh frolics was actually fun. Now, I have some first-hand experience of Italy, and also of posh people, but I know absolutely nothing about the world of acting and celebrity. So the toxic world of "Let's Pretend" was a bigger challenge. Luckily, in the age of Instagram, the lifestyles of the rich and shameless are more accessible than ever before - though, of course, it's what lies behind the glossy facade that's really interesting. I did some fact-checking with a friend of mine who’s a celebrity agent and I can assure you that while the novel is pure fiction, my background research is both impeccable and unpublishable.

Ada in The Favour and Lily in Let’s Pretend both aspire to improve their social status and get rich. What is different in the ways they target their goals?

Ada is a social climber because she feels the life she was born to was ripped away when her adoptive father died. Ever since, she’s been adrift. She’s clever and sensitive, but uses these skills to insinuate herself into the charmed lives of the public school elite. The tension in her story comes from her awareness that these people aren’t actually worth the effort – there are moments when she realises what a mess she’s in, and how flimsy the rewards really are. So she’s certainly not beyond redemption … but when it comes to the crunch, will she do the right thing? Lily is less self-aware and much more self-loathing than Ada. She’s a faded ex-child-star who is manipulated and bullied by her mother, and condescended to by her more successful relatives (she’s from a famous acting family). So her fight to get into the limelight isn’t so much because she craves wealth or celebrity, but because she’s scared of never escaping her past failures and never becoming a “real” person. She latches onto a fauxmance with Adam because they’re both damaged people looking for meaning in their lives, and over the course of the book their relationship becomes more complex than a merely transactional one.

Both books feature poor communication between mothers and daughters. Why did you make this an integral part of the plot?

I’m lucky to have a lovely relationship with my mum, but I do appreciate that mother-daughter dysfunction can be one of the most toxic kinds. At least Ada’s mother is generally trying to do the right thing: she sees that Ada is delusional and heading for a fall, but her warnings fall on deaf ears because her tone tends to be exasperated or dismissive rather than understanding. Lily’s mother the “momager” is mischievous and fun-loving and you could imagine going out for cocktails with her and having a ball. But she’s also incredibly poisonous. She encourages all Lily’s worst impulses and every compliment comes with a sting in the tail. So if you read both books, I think you’ll be yelling “Listen to your mother!” to Ada and “Ignore your mother!” to Lily.

Ada in The Favour reminds me of Becky Sharp in Vanity Fair. Have any classic novels inspired your writing?

I love nineteenth-century novels and appreciate the Vanity Fair reference – it’s been a favourite of mine since I was a young teenager. I also re-read most of Austen every year. Come to think of it, perhaps this is one of the reasons my crime fiction has a slightly satirical edge! Austen would have been a fantastic crime novelist: her cynicism and wit, her rigorous moral compass, her scathing critique of social mores and moral hypocrisy… I get very cross when people dismiss her books as rom-coms. She understood the dynamics between the powerful and the powerless like nobody’s business.