From Doctor Who to Friends: what does a relationship expert make of TV's most famous couples?

The potential problem: If opposites attract, then...

Susan says: “Irene and Sherlock are very, very similar. A thing with a sociopath is that they can't step into anyone else's shoes. They are in the centre of their own world so they have no shame doing what they want to, they have no shame about lying, they can be extremely charming to get what they want but when they're not interested they can be cold and distant. They're emotionally mature, but completely obsessed with themselves. If anything, it's Watson that Sherlock treats like his wife!”

Would it work? “He really goes out of his way to save her life [at the end of A Scandal in Belgravia] and really must've put himself out. Will they ever have a normal relationship? Absolutely not. But there's an irresistible attraction.”

Piper Chapman and Alex Vause (Orange is the New Black)

Who? Piper is the middle-class Pollyanna of prison, who finds herself locked up with her hard-edged ex-girlfriend, Alex. They soon rekindle their romance.

The potential problem: Can a relationship survive the pressures of prison?

Susan says: "When there's a sense of anxiety and danger, people get together more easily. It becomes an infatuation. You get it a lot on I'm a Celebrity... Get Me Out of Here!, or Big Brother – anywhere with closed situations, where there's a lot of pressure. It's very common for people to get together when it's 'us against the world'."

Would it work? If you meet in a high pressure situation, then you get out, there's a high likeability you'll fall apart. The outside threat has gone, you don't need to cling together in the same way. That basic incompatibility may not have been apparent because they clung to each other so much in prison."

Mulder and Scully (The X-Files)

Who? A couple so iconic Catatonia wrote a song about them: a pair of FBI special agents who fall in love after years of romantically investigating freaky aliens together.

The potential problem: But can you really work together and be together?

Susan says: “Working together as a couple can be wise, as you're seeing a lot of wide varieties of behaviour at work rather than two date nights a week. You've seen a big variety of who they are and you want that. However, it has some really strong built-in disadvantages. If you fall out of love with them, who gives up their job? It's much easier to hold down a good relationship if you're not working together so closely.”

Would it work? One of the things that makes a relationship work is the amount of time you're together and you're apart, and there's no rule about that – it's about what amount makes you happy. But if you've had a horrible day at work, for example, you're having that horrible day with them. And then you get home and you refer things back to work, and it can tarnish things.”

Lucious Lyon and Cookie Lyon (Empire)

Who? The aptly named Cookie Lyon is a ferocious songwriter with a ferocious personality, while her husband Lucious is her greatest creation: a superstar rapper. Together they have three kids and a huge musical empire.

The potential problem: Lucious is a bona-fide criminal, and his marriage abruptly ends when Cookie takes the rap during a botched drug trade. Now out of prison, she finds Lucious has taken over their business and moved on. Could a marriage ever recover from such a sacrifice?

Susan says: “When you make a sacrifice, it makes the other person owe you. So one person has too much power in the relationship and it can fall apart. What's Luscious going to do [if they get back together]? Spend all his life going, “I'm sorry, thank you so much” etc? Or is he going to get tired of that? It's not fun to be guilty for the rest of your life, and it's not fun for her to be angry for the rest of her life. So if you don't get therapy it's a living death for both of you.”

Would it work? “If you're lost in another world, like prison, you can change. And if you then get back together, your values are different, and the whole thing falls apart.”

Buffy and Angel (Buffy the Vampire Slayer)

Who? She's a teenage vampire slayer, he's the 200-ish year-old vampire with a soul.

The potential problem: If Buffy and Angel have sex, then Angel loses his soul, transforming him back to one of the most evil vampires who ever lived. You know, the usual.

Susan says: “A relationship that begins with an agreement that there is no sex is very, very unusual. Not only because there's usually a sexual attraction in couples, but being together, having sex together, is not only a sign of commitment but creates commitment. When we use the expression 'making love' we are talking literally. You have sex with someone, physiologically, psychologically there's a shift in the hormones, a shift in the brain chemistry, that makes you think, 'You matter.' On the other hand, if both parties agree, it's okay, and it's possible.”

Would it work? “There are lots of perfectly good relationships where sex is in the past. However, if you're going to start a relationship with no sex ever, it has to be very carefully negotiated.”

Carrie Bradshaw and Mr. Big (Sex and the City)

Who? She's a shoe-obsessed, materialistic sex columnist, and he's a hotshot tycoon who makes money doing, like, business and stuff.

The potential problem: They're both as bad as each other, really. Despite constantly breaking Carrie's heart, the commitment-phobic Mr Big always wanders back into her life, and human doormat Carrie always lets him – even to the point of having an affair when she finally finds someone else.

Susan says: “They're destined to be on and off forever because it's so exciting. It's this whole thing of, 'Oh my god it's all coming to an end, weep weep, moan moan!' And then, 'Oh it's starting up again, now it's going to be OK.' Without going into psychological theory too much, this can be attractive. It can be literally like a drug, like an addiction. There's this whole thing called approach and avoidance behaviour, where you come really close, then you can't live with each other, then you pull back. And when you pull back, suddenly: 'I want you again.'

Would it work? “So will they still be together? Yes they will. But would they ever really be able to live together? No. They'll either tear each other apart and break up, or it will be more and more boring and they'll lose interest, and start affairs with other people.”

How to Choose a Partner by Susan Quilliam is out now