Vengeful wives are said to be turning to post-nups to punish their straying husbands. But there are other reasons why married couples might want to spell out how assets are divided on divorce

For Maria, her husband’s infidelity no longer causes her pain, because her revenge gives such phenomenal and perpetual delight. She married for love but it turned out her husband thought that the life he paid for, “the houses, the holidays, the cars and, yes, the yacht – was so important to me that he could behave like a rutting stag and I’d never leave him,” she says. “He was speechless when he realised that I genuinely intended to walk away. He went into a sort of decline.”

Maria pauses and giggles. “His reaction was, shall we say, rather unexpected given how much extra-marital shagging I’d discovered he’d been up to over the years. But it was most useful in helping me plot my course of action.”

Maria told her husband she’d stay with him on one condition: the couple would open up their pre-nup. “Not ‘renegotiate’ the pre-nup,” she says. “This time, it was me doing all the talking.”

If her husband strays again, it will cost him dear: the fair split agreed on before their marriage is now heavily skewed in Maria’s direction. “It’s the financial equivalent of castration,” she says, calmly. “I get so much he’ll be left with nothing to buy his next floozy.”

Maria is blazing a trail: betrayed and vengeful wives are increasingly turning to the “post-nup” to punish their straying husbands. Toby Atkinson, a partner in the divorce and family department of Stewarts Law in London, says that he increasingly has clients asking for a post-nup to keep their marriages together. “We have had a marked year-on-year rise in terms of the number of clients we have acted for who have entered into post-nups. We are probably doing three to four times as many as we did five years ago.”

I am not perfect, but I am very rich. Russian courts wouldn’t make it worth her while for my wife to leave. It’s different here

Just like its older sibling, the pre-nuptial agreement, the post-nup spells out how a couple’s assets are distributed in the event of divorce or death. The difference is that a post-nup, as the name suggests, can be undertaken at any time after the marriage has occurred. Like pre-nups, post-nups aren’t legally binding but they do carry weight in British courts, providing they have been signed by both parties without duress and alongside legal advice.

In a 2015 survey by the American Academy of Matrimonial Lawyers, half of divorce lawyers cited an increase in spouses seeking post-nuptial agreements during the past three years. The trend has now arrived on our shores, largely taken up by wealthy couples struggling to keep their marriages together.

The usual scenario, says Atkinson, is the husband has been unfaithful to his wife and she says to him: “I will stay in this marriage, but it’s going to be on my terms and it’s going to cost you.”

For Ayesha Vardag, signing a post-nup with her husband was a “very public celebration of our independence and love for each other”.

“We signed our post-nup among our friends and family at the reception with great fanfare, having married in Winchester Cathedral,” she says. “We wanted to make a statement: we both believe very strongly in couples’ rights to agree their own affairs as independent individuals, not hand them all over to the state to sort out for them.”

Vardag, one of the UK’s highest-paid divorce lawyers, says her own post-nup deals not only with the finances but also with the country in which she and her husband would like the divorce to go through, with confidentiality, social media rules and steps to avoid any ill-will or blame in any divorce petition, despite the fact that English law forces couples to identify which party is at fault. “It covers lots of things that we want to agree between us and not leave to chance,” she says.

Facebook Twitter Pinterest German paper company heiress Katrin Radmacher won her pre-nup case at the supreme court after Nicolas Granatino’s divorce settlement was slashed from more than £5m to £1m. Photograph: Luke Macgregor/Reuters

Another reason for the increase in post-nups in Britain is the growing number of international “ultra high net worth individuals” – defined as those with more than $30m in liquid assets – moving to London with their families. The city has become the “divorce capital of the world” thanks to English law’s favourable attitude towards the non-wealth-creating spouse – usually the wife – and this migration has led to a growing number of extremely high divorce awards, many in the hundreds of millions. “Many wealthy individuals are wising up to the risk and are insisting on formal marital agreements with their spouses before moving here, specifically to protect their assets should their partner issue divorce proceedings,” Atkinson adds.

There is another advantage to the richer spouse in having a post-nup, says Sandra Davis, head of Mischon de Reya’s family department who specialises in pre- and post-nuptial settlements involving couples with a net worth of between $1 million and $30 million. “I’m negotiating a post-nup at the moment,” she says. “I find they are often a precursor to divorce where the wealth creator in the marriage is seeking to get away with paying less than he or she would pay if the matter was to litigate, because, in court, they would have to give full disclosure as to their real worth.”

But a post-nup can lead to marital breakdown even if that wasn’t the intention. “Do I often see a post-nup lead to divorce? When you put something on the table, you give it legs and then it can walk away by itself. Couples can very quickly fall into contention when talking about dividing assets.”

Alexei signed a post-nup with his wife of ten years. “I am not a fool. My wife is considerably younger than me and, what can I say, I am not perfect,” he says. “But I am a very rich man. In Russia, the courts wouldn’t make it worth her while for my wife to leave me. But here it’s a different story.”

Alexei admits he sprung the post-nup on his wife before she knew of his plans to relocate the family to London. “I told her that I’d been looking at our pre-nup and wanted a new agreement because I loved her and wanted to give her more,” he says. “I do love her. But, as I say, I am not a fool.”

The impetus to sign a post-nup is not always so soul-destroyingly one-sided. Catherine Costley of the London law firm Payne Hicks Beach, says the post-nup is increasingly used when both members of the couple are earning but decide one partner, probably the mother, is going to give up their career to take care of the children. In cases where one partner’s earning capacity will have been significantly diminished, a post-nup is a “sensible and reasonable act”, she says. “As a professional woman, you won’t make that time back. You can’t just walk back into your high-flying career four, five, 10 years down the line. You wouldn’t take a new position without compensation in your business life, so why do it in your personal life?”

Julia, who met her husband when they were both working for a hedge fund, agrees. “I actually earned slightly more than him but when children came along we agreed you couldn’t have two parents working the crazy hours we worked,” she says. “So I took four years off then went back on a much lower rung of the ladder.

“This was a joint decision we made but we were both aware that I was the one taking all the risk, and that wasn’t fair. We thought of [the post-nup] like life insurance. We’re still very much in love and very much a couple, but we’re grown-ups, too, who need to protect our children, and protecting ourselves against worst-case scenarios is the best way of protecting them.”

Some names have been changed