The book divided public opinion, as it was viewed by some as empowering women to take control of their dating lives, while others saw it as promoting manipulative and outdated gender roles.

 The book's authors, Ellen Fein and Sherrie Schneider, advised women to follow strict dating rules, such as not calling or texting first and always letting the man make the first move. 

Despite the controversy, the book became a bestseller and inspired a series of sequels and spin-offs.

Critics lambasted The Rules that seemed like antiquated advice even 30 years ago: don't talk to a man first; don't ask him to dance and always end the date first.

Others said the book encouraged women to 'toy' with men and manipulate them, advising 'don't call him and rarely return his calls' and 'don't meet him halfway or go Dutch on a date'. Yet it was an instant bestseller, shifting four million copies in 27 languages and capturing the popular imagination.

The Rules prompted references on TV's Sex And The City and screaming debates on Oprah. 

Beyonce admitted it 'worked for me', while actress Blake Lively apparently used The Rules to snare Leonardo DiCaprio (they dated for five months). When Princess Diana was linked to rugby player Will Carling, his then wife Julia made headlines by offering on live TV to send her the book (Rule 23: Don't date a married man). Meghan Markle was reported to have studied the book and put it into practice (more of which later).

Now, authors Ellen Fein and Sherrie Schneider are back with a new, updated guide, The Rules Handbook. And it's more controversial than ever.

If the original Rules were about 'capturing his heart', today Sherrie and Ellen, 63 and 65, are advising on how to keep a man happy and committed in a long-term relationship, too.

Beware: the new guide may send your blood pressure soaring. Take this example. 'When your husband says something stupid, say nothing back. Two wrongs don't make a right. Practise silence!'

Or: 'When you come home from work where you have a fancy title like senior VP of corporate marketing and investor relations and run a staff of 50 people, switch from masculine to feminine mode. Set the table and cook dinner, and ask him nicely to help clean up!'

Or this: 'Just like dating isn't 100 per cent equal (the guy has to pursue you and propose), marriage isn't always either. [You must] both agree your husband/partner is the decision maker and you are his key supportive team member... even if you make more money.

'That's because romantic relationships are based on biology, not finance. There's a hierarchy that goes back to caveman days. If you act too bossy or overbearing, you will emasculate your husband and your marriage will suffer, so let him take the lead role.'

Does such advice really have a place in the 21st century?

'We're making it like he's the senior partner and you're the junior partner,' Sherrie explains. 'Sometimes, you'll be senior like if it's a kids' issue, or if you're better with money or better with organising.

'But we're saying, in general, men are born leaders. This is biological. It's based on our experience and that of our clients, and biology states that men are born to lead and women are more the nurturers, even though they're in powerful positions in their work life.'

She cites the example of Eileen Ford, who co-founded the famous Ford Models agency with husband Jerry. 'When we interviewed her, she said: "When I walk through the front door, Jerry's the boss."'

'That's how you have to make a man feel. You can say it's controversial, it's awful, but that's the reality. A lot of people say it shouldn't be that way, but that's a lot of magical, wishful thinking.' She adds: 'You have to be feminine even if you're a CEO because no man wants to be with a woman who behaves like a man.'

Though many will find the gender roles here old-fashioned, others would argue that the 'traditional' marriage is far from dead. On social media platforms such as TikTok, the 'trad wife' movement is trending among young women.

Speaking on Zoom from homes in New Jersey and New York state's Long Island, Sherrie and Ellen still sport the long, straight hair they championed for Rules Girls in their original book (men prefer it, apparently).

As well as writing books, they offer personalised advice in person or over the phone — a 15-minute consultation costs $150 (£120). A six-hour package will set you back $1,500 (£1,200).

'We also do makeovers,' says Sherrie. 'A lot of women don't know how to dress for a date — they look like Diane Keaton with the turtlenecks and short hair and slacks. For clients in their 20s, 30s and 40s, we tell them mini skirts.'

In some ways The Rules for marriage are directly opposed to the 1995 Rules for dating and 'snaring' a man. Where the latter emphasise 'being hard to get', the former prioritise above all else 'being easy to live with'. Even when he's not.

'If you're not married,' Sherrie tells me, 'maybe you'll find that shocking, but if you are married, you'll know exactly what we're talking about. The self-control that was used to date him is now used to keep him.'

Can they define what makes a husband happy? 'Every husband we know loves food and loves to be fed,' says Sherrie, 'so make sure they're fed and keep your refrigerator stocked. Go out to dinner if they want to. And obviously, intimacy is important to men, most men. Just be cordial and kind.'

Should a wife say yes to sex, even if she's not up for it?

'You should try to,' says Ellen, 'but you don't have to say yes if you're not in the mood.'

Sherrie adds: 'I think with intimacy what we say in the book is that you're not always in the mood to do other things. I'm not always in the mood to exercise, but on some level, it's less work to just do it than to fight it, you know!'

'Every couple is different but most women are not as into it as men. So, getting meals, having intimacy, being a family, going on family vacations, these are all important.'

Then something unexpected happens. Ellen suddenly announces she's not in the mood for this interview. 'I don't really want to be quoted talking about sex,' she says. 'I'm uncomfortable. I never talk about sex.'

But 'intimacy' is discussed often in the book?

'I think Sherrie's doing a great job,' she says, 'so I think I'm going to hang up.' And… she's gone.

Ellen, it transpires, has just 'had some dental work done', leaving Sherrie to explain some of the book's more eyebrow-raising assertions.

'Intimacy and cooking are to men what snuggling is to women,' reads the tip titled Make Time For Intimacy, for example. 'One benefit of a Rules Marriage is that your husband finds you attractive and loves your cooking, so be flattered. Try to put yourself in the mood because it's not about feeling it all the time, but doing it. Physical intimacy leads to emotional intimacy. Everyone wins!'

It's hard to see how women can win if they're constantly putting themselves last, demoting their needs, prioritising his. Frankly, that sounds more like a recipe for marriage-killing resentment.

Women, they write, should in no way attempt to control or change a man. 'A woman really can't tell a man what to do in the same way a man can tell a woman what to do, even though it doesn't sound politically correct,' says Sherrie, who seems unfazed by Ellen's exit. She cites the rather unrepresentative example of Michelle Obama, who didn't want Barack to run for president. The wives who don't give in get divorced.

'It sounds unfair,' she admits, 'but when the wives let their husbands do whatever they want and be themselves, then the husbands reciprocate in kind.'

In what way? 'It could be anything, like if you let your husband watch TV, he will let you buy a dress, or something,' she explains. 'It will come back in some way because he'll just feel like you're not a ball and chain.' Nagging, naturally, is verboten, as is 'the D Word' — divorce ('say it enough and your husband will say it back'). The underlying premise here is that divorce is the catastrophe a woman must avoid at all costs. Should the husband offer his spouse 'correction' by putting a stop to her out-of-control spending habits or demanding more home-cooked meals instead of takeaways, then instead of getting cross or looking up D Word lawyers, she should think of her husband as her 'biggest helper'.

So why is the wife making all the compromises? She's not, says Sherrie — she's playing a cannier game than that. 'You have to be diplomatic, strategic, know when to push and when to be quiet. You can't just be all yourself. We're not saying you should be deaf, dumb and blind. You just have to pick your battles — that's one of our Rules. Maybe your husband is a slob, but he's also making a ton of money and is always playing soccer with the kids.'

Childcare, she admits, does fall naturally on the woman. You should expect a man to pull his weight, but there are limits. Most husbands are pretty involved. He's not going to change [nappies] but he's going to take them to soccer. The problem is focusing on the thing you're not getting. And you don't get everything.'

It's all a far cry from the ballsier, no-nonsense Rules Girl of yore who never accepted a Saturday night date after Wednesday and who always ended phone calls after ten minutes. While the Rules Girl demanded to be treated like a goddess, the Rules Wife, frankly, sounds a bit of a doormat.

'We're really not telling women to be doormats,' Sherrie insists. 'We're just saying it's easy when you're angry to go over the top and say things you regret and we say to clients, press the pause button. Women are more emotional than men, so I'll try to discuss an issue with someone else before I go to my husband because I know if I talk about it enough beforehand, by the time I approach him, it's calm. When you have an issue,' she adds, 'think to yourself: do I want a short-term benefit where I get to yell, or do I want what's good for the marriage? I don't feel subservient at all. Men do a lot of things that go unnoticed, like taking the car to the mechanic.

'I do know our marriage is better when I kind of go along with my husband's flow. For instance, he wanted to see Jerry Seinfeld's show live, but I didn't want to leave the house because it was cold and because I waited too long, we didn't get the tickets.

If he was my boss and he'd asked, I would have said yes immediately because, well, it's the boss. It was a bad call.'

Seinfeld tickets aside, The Rules clearly work for Sherrie. She has been married to her businessman husband for 29 years (she prefers to keep his name private) and they have a 26-year-old daughter who has basically been doing The Rules from the womb.

'I was pregnant with her when we were on Oprah and because she's seen me talking to clients and appearing on TV, she knows The Rules and does them. Even when she was a teenager she didn't see it as old-fashioned because a lot of her friends did not do The Rules and she would see the heartache.'

Occasionally, though, even a Rules marriage can go off the rails. Deal-breakers for a wife include drink and drug abuse (unless he's willing to go into rehab), physical violence and infidelity.

'Sometimes the wife is ignoring the husband and if he's on a long-distance trip and sleeps with somebody and it's completely meaningless and then afterwards, he begs his wife for forgiveness, that's different,' says Sherrie.

'We've seen that with a client and she took him back and everything was completely fine. But that's very different to sleeping with someone else for a year and having a separate life. That's probably unforgivable.' Should divorce ensue, 'take the high road,' counsels the book. 'Don't play the blame game or badmouth him.'

Now would have been the perfect time to ask Ellen about her own divorce from first husband, Paul Feingertz, after 16 years of marriage and two children, now aged 32 and 35.

In 2001, while legally separating from Feingertz, Ellen admitted she'd broken the very rules she co-authored, especially Rule 28: Have A Date Night ('my husband was a big goer-outer. He loves date night, but the girl who fought so hard to have date night on Saturday night was just too tired to go out on Saturday night').

Later, over email, she writes: 'We simply grew apart and are the best of friends.' In 2008, she married for a second time, to entrepreneur Lance Houpt.

How soon should a woman date after a divorce? 'Immediately,' says Sherrie. 'There are plenty of hours in the day to grieve — you're not going to be on a date for 24 hours, so you can cry in the supermarket or while doing Pilates. It sounds cold-hearted but it really works.'

I ask Sherrie about Meghan, who before her wedding to Prince Harry was described by the duo as embodying 'everything we say about being princess-like and feminine, classy, discreet and confident'? Sherrie pauses. 'Well, this is the thing: she said that in high school and college everybody talked about The Rules, so I do believe she knew them.'

The first book included tips for snaring a VIP including 'don't show any interest in his career' and 'don't seem overly interested in his wealth or the limelight'. 'Rules Girls are not groupies.' says Sherrie. 'I do believe she applied some of our Rules for dating a celebrity to Harry by saying: "I didn't know who Prince Harry was."

'That's impossible! I believe she knew exactly who he was. So, Meghan did the celebrity Rules very well and I believe she ended the date first too.'

But since then? Has she become a Rules Girl gone bad? 'I'm sure she's a good wife to him,' says Sherrie, 'but what she did on Oprah and putting down the Royal Family, that's completely not the Rules for marriage. She shouldn't have said anything negative about his family.'

It's hard not to react with disbelief at some of the advice dispensed by Sherrie and Ellen, but the duo remain unbowed. 'We are feminists,' Sherrie insists. 'We believe that feminism is about equal pay for equal work and better opportunities.

'Ellen and I have our own company and no man is involved in that. We just don't think that believing men are masculine and women are feminine by nature and that romance works better when men make the first move is anti-feminist. We think it's realistic.'

One can't help feeling that the Rules belong to a bygone era, where marriage was a woman's most important goal in life.

In a world where gender roles have shifted dramatically, do women need The Rules? According to Sherrie, they still do. 'We might not be telling women what they want to hear,' she says, 'but we want to tell women the truth.'

The Rules Handbook by Ellen Fein and Sherrie Schneider (DeVorss Publications) is out later this year.