Cross-border divorce and child custody battles and business disputes could become messier and lengthier unless Britain can secure agreement to maintain judicial co-operation arrangements with the EU after Brexit.
In a paper published ahead of the third round of formal Brexit talks in Brussels next week, the UK Government says that it is "vital" for millions of families, businesses and consumers for Britain and the EU to agree "coherent common rules" for civil cases following withdrawal.
The UK is seeking a new arrangement which would "mirror closely" the sophisticated EU system for deciding which country's court should hear a civil, commercial or family dispute raising cross-border issues, whose laws should apply and how any decision should be enforced.
If Britain leaves without a deal, UK citizens could find themselves forced to fall back on international rules set out in agreements such as the Hague Convention, which officials acknowledge are slower and less effective than the EU system.
And rival sides in a dispute could end up launching court cases in the UK and another EU state without agreement on which ruling is definitive.
The problem could affect Britons involved in divorce, custody and child maintenance battles with EU-born spouses, companies suing continental suppliers or consumers seeking compensation for faulty European goods.
The European Commission has so far set out proposals only for dealing with cases already under way at the time of Brexit, and Brexit Secretary David Davis is now pressing for early discussion on the arrangements for co-operation after the UK leaves the direct jurisdiction of the European Court of Justice.
Announcing plans to seek "new close and comprehensive arrangements" for civil judicial co-operation with the EU, reflecting "closely" the existing rules, the UK Government paper states: "We have a shared interest with the EU in ensuring these new arrangements are thorough and effective.
"In particular, citizens and businesses need to have continuing confidence as they interact across borders about which country's courts would deal with any dispute, which laws would apply and to know that judgments and orders obtained will be recognised and enforced in neighbouring countries as is the case now."
The paper states that the current EU arrangements deliver "predictability and certainty" and play "an important role" in enabling businesses to trade with confidence across borders, providing legal certainty in cross-border transactions and avoiding delays and excessive costs in family cases.
"The best way to ensure legal certainty for both UK and EU citizens and businesses as we leave the EU is to facilitate a smooth transition to a new relationship in civil judicial co-operation," it says.
In order to allow citizens and businesses on both sides to plan ahead, both the UK and EU would benefit from "an interim period that allowed for a smooth and orderly move from our current partnership to our future partnership".
The paper makes clear that the UK intends to apply for membership as an individual country of international judicial agreements in which it currently participates through its EU membership, including the Hague Conventions and the Lugano Convention.
Labour MP Wes Streeting, a leading supporter of Open Britain, said: "The Government's hypocrisy on this issue is mind-boggling.
"It is they, not the EU, who have said repeatedly that no deal is better than a bad deal. And yet now they admit that a Brexit with no deal on judicial co-operation could put British children in legal limbo.
"Ministers need to drop their absurd rhetoric about no deal, and focus on negotiating an agreement with the EU that guarantees British families and children will not lose rights and protections as a result of Brexit."
The national chairman of the Federation of Small Businesses, Mike Cherry, said: "Commercial business-to-business disputes that take place across borders with EU27 countries, such as on late payments, must have quick and easy remedies to shore up small business trading confidence.
"Small businesses will need time to adapt to any new changes and therefore clear and early communication will be essential once an agreement has been negotiated with the Commission. This will be necessary to avoid a dip in confidence, which might then be followed by a dip in levels of trade."
Liberal Democrat Brexit spokesman Tom Brake said: "This exposes the reality of a no deal Brexit - abducted children at greater risk and families plunged into uncertainty.
"The Government needs to end its heartless insistence that no deal is better than a bad deal. Avoiding the devastating human consequences of an extreme Brexit should come ahead of the ideological obsessions of Tory Brexiteers.
"The Conservatives claim to be the party of family values, but their plans would risk tearing more families apart."