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.
