Four categories of clause will not be enforced by a court in England and Wales, however carefully you draft them: anything that determines arrangements for children, anything that would leave one partner reliant on state support to get by, non-financial or lifestyle terms that have nothing to do with money, and terms so one-sided that the whole agreement fails the fairness test set out in Radmacher v Granatino [2010] UKSC 42. Writing any of these into your prenup does not make the document illegal. It makes those specific clauses dead weight a judge will simply ignore, and in the worst case, it can make a judge look harder at the rest of the agreement too.
This is the one article in this series where getting it wrong costs the most. A prenup with an unenforceable clause quietly sitting inside it is not a bigger problem than not having a prenup at all, but it can create false confidence: you believe a point is settled when a court would treat it as though it were never written. Read this before you finalise anything, and if a clause you want to include is not covered below, ask your solicitor specifically whether it is enforceable rather than assuming it is.
1. Anything that determines arrangements for children
A prenup cannot decide, in advance, who a child will live with, how much time they will spend with each parent, or how much child maintenance will be paid. This is not a drafting weakness that better wording could fix. It reflects a jurisdiction that cannot be contracted away. Under the Children Act 1989, a court's duty is to treat a child's welfare as its paramount consideration when any decision about that child is made, and it assesses that at the time the decision is needed, not based on what two adults agreed years earlier, possibly before the child even existed. Source: Trust Family Law, "What Cannot Be Included in a Prenup UK?".
Child maintenance runs into a similar wall from a different direction. In most cases, jurisdiction over child maintenance sits with the Child Maintenance Service under the Child Support Act 1991, not with a private contract between parents. Parents can agree maintenance privately, and many do, but that private agreement does not permanently remove either parent's right to apply to the CMS if it stops working, whatever a prenup might say about it.
None of this means a prenup cannot mention children at all. Plenty of agreements record what the couple currently intends, as a statement of intention rather than a binding term. What it cannot do is bind a future court, or a future version of either parent, to a specific arrangement decided before anyone knows what the child will actually need.
2. Clauses that would leave one partner dependent on the state
The fourth Radmacher condition asks whether the outcome is fair when the marriage ends, and a court's idea of fairness has a floor: an agreement that leaves one partner unable to meet their basic needs, so that they would have to fall back on state support to live, is not one a court will enforce as written, no matter how cleanly the rest of the document was drafted.
KA v MA (Prenuptial Agreement: Needs) [2018] EWHC 499 (Fam) shows how this plays out in practice. The couple's prenup, signed three weeks before their wedding, would have limited the wife to roughly £1.6 million. The High Court held the agreement should still carry weight, but increased her award to £2.95 million because the prenup's terms did not meet her actual needs at the point of divorce. Source: Family Law Week, "KA v MA (Prenuptial Agreement: Needs) [2018] EWHC 499 (Fam)".
The lesson is not that needs-based clauses always fail. It is that a term deliberately designed to leave one partner with nothing, or with less than they need for housing and basic living costs, will not survive contact with a court, and a needs shortfall is exactly the kind of thing that later gets litigated, at cost to both of you.
3. Non-financial or lifestyle clauses
Terms with nothing to do with money or property are not the kind of thing a family court's financial remedy powers can enforce at all. Clauses that come up in practice, and get struck out or simply ignored, include penalties for infidelity, requirements about household chores, how often the couple takes holidays together, or expectations about weight, appearance or other personal conduct. Source: Trust Family Law; similar examples appear in Prenuptial Agreement Solicitors, "What Can and Cannot Be Included in a Prenup".
These clauses are common in prenup templates written for other countries, particularly the United States, where some states do enforce lifestyle terms in certain circumstances. Copying a template that includes them into a UK agreement does not make them enforceable here. At best they are ignored. At worst, a document padded with unenforceable personal clauses can look less serious to a judge assessing whether the couple approached the whole exercise carefully, which is one more reason not to include them even as a joke.
4. Terms so one-sided they fail the fairness test
Even a prenup that meets every procedural condition, full disclosure, independent advice, no pressure, can still fail on substance if the outcome is grossly unfair. The Supreme Court's own words in Radmacher are the standard every solicitor drafts against: a court should give effect to an agreement "freely entered into by each party with a full appreciation of its implications unless in the circumstances prevailing it would not be fair to hold the parties to their agreement" (paragraph 75). Source: Supreme Court of the United Kingdom, Radmacher v Granatino judgment; full text also at BAILII.
A term that leaves one partner with literally nothing after a long marriage, or where children were raised together, is the clearest version of this. Less obvious versions include an agreement that never accounts for one partner having given up a career, or one that ring-fences everything either of you will ever earn during the marriage, not just what you brought into it. The fairness test is assessed at the point of divorce, with the benefit of hindsight over how the marriage actually played out, so a term that looked reasonable to two people in love before the wedding can look very different to a judge years later.
What this means for the rest of your prenup
None of the above makes a prenup pointless. It narrows what the document should actually try to do: record what each of you owns and owes, agree how you will treat it if you divorce, and leave children, state dependency, lifestyle expectations and one-sided outcomes out of it entirely. A prenup built on those terms, with the four Radmacher conditions properly met, is the version most likely to hold up. See are prenups legally binding in the UK for the full conditions, and postnuptial agreements in the UK if you are already married: the same restrictions in this article apply to a postnup exactly as they apply to a prenup.
Scotland again is different
Scotland applies its own statute, section 16 of the Family Law (Scotland) Act 1985, and Scottish courts assess fairness at the point of signing rather than at the point of divorce. The categories in this article, particularly the point about children, are not Scotland-specific: no jurisdiction in the UK lets two adults sign away a court's role in a child's welfare. But how a Scottish court weighs a one-sided financial term can differ from the England and Wales approach above, so if either of you has Scottish ties, get advice from a solicitor qualified there specifically.
Ana and Rafael's near miss
Ana and Rafael's solicitor sends them a first draft based on a template Rafael found online. It includes a clause saying Ana would receive nothing if she was ever unfaithful, a clause requiring both of them to take at least one holiday abroad each year, and a clause stating that if they divorced, all future earnings for both of them would stay entirely separate, with no adjustment regardless of whether either of them left work to raise children.
Their solicitors flag all three. The infidelity and holiday clauses are removed outright, since neither has anything to do with the financial terms a UK court can enforce. The earnings clause is rewritten: pre-marriage assets stay separate, as Ana and Rafael intended, but anything built jointly during the marriage, including adjustments if one of them reduces paid work for children, is shared. The final agreement is shorter than the template, and every clause that remains is one a court would actually look at rather than skip past.
Common mistakes
Copying a US-style template. Lifestyle and conduct clauses that might mean something elsewhere are dead weight in an England and Wales agreement, and can make the rest of the document look less considered.
Trying to lock in child arrangements now, "just in case." It will not bind a future court. Focus the agreement on money and property, where it actually has force.
Leaving one partner below a basic standard of living, on paper, on purpose. This is the fastest way to have the entire agreement revisited under the fairness condition, not just the offending clause.
Assuming an unenforceable clause is harmless filler. It is not neutral. A document that reads as one-sided or careless in places can undermine confidence in the parts that would otherwise hold.
Not asking a solicitor to review every clause individually. Some terms look financial but are not, a clause tying money to conduct, for instance. A solicitor spots the difference; a template does not.
Speak to a solicitor before you finalise anything
Every point above is a general description of how English and Welsh courts have treated these categories of clause, not a substitute for advice on your specific agreement. This article is informational and does not replace independent legal advice from a solicitor qualified in the jurisdiction that applies to you. eziduo is not a law firm and does not provide legal advice. If a clause you want to include is not covered here, do not assume it is safe: ask your solicitor before you sign, since independent legal advice is itself one of the conditions that gives the rest of your prenup its weight.
Keeping your prenup to what a court will actually enforce, money and property, is also the part of it that overlaps with day-to-day life afterwards: a shared, accurate picture of what you each have. eziduo is built around exactly that kind of ongoing view for couples, separate from anything a solicitor drafts, but useful groundwork for the disclosure a prenup requires in the first place.
No stress
