Parents in the UK would find it “much more difficult” to recover abducted children if Britain fails to persuade the EU to continue legal cooperation after Brexit, according to government officials detailing their latest plans.

Officials said the process of appealing to foreign courts for help could become much more complicated, when asked about a hypothetical case of a child of a British parent being taken out of the country by a spouse from another member state as an example.

Unusually, the latest UK policy paper, dealing with cross-border civil judicial cooperation, contains a lengthy section outlining what might happen if Britain walked away from Brexit negotiations without striking an exit deal.

The section, which was included at the request of Brussels negotiators, makes clear that the UK would be forced to rely on existing EU rules for wrapping up outstanding court cases but would then have to fall back on less effective arrangements under international treaties such as the Hague convention.

“It would be much more difficult [to get a child back],” said one official. “There are a range of time measures. The fact is none of these systems are as effective or speedy as the current arrangements we have or the future ones we want to agree.”

The case is just one example of the complex web of legal relationships enjoyed by Britain under its existing EU membership and was cited as a reason why the new government’s strategy is largely to emulate as much of the existing cooperation agreement as possible when Britain leaves.

“The world is more interconnected than ever and families increasingly come from more than one country – there are approximately one million British citizens living in other EU member states and some three million EU citizens living in the UK,” explains the position paper. “When things go wrong, families need to know that they will be able to resolve disputes in a clear, predictable way, without undue delay.”

The paper also confirmed that a reciprocal deal would involve foreign judges being able to exert authority over British citizens, despite Theresa May’s past insistence that Brexit would exclude Britain from the rulings of foreign judges.

“We will not have truly left the European Union if we are not in control of our own laws,” the prime minister said in the Lancaster House speech that set out her Brexit strategy in January.

Since making that speech, the government has come under pressure from the legal industry to preserve close collaboration with the EU to protect London’s role as an international centre for dispute resolution.

Tuesday’s paper describes the existing EU cooperation agreement as “an unprecedented position of close integration” and says the UK wants to negotiate a replacement that “reflects closely the substantive principles”.

“Existing international conventions can provide for rules in some areas, but they would not generally provide the more sophisticated and effective interaction, based on mutual trust between legal systems, that currently benefits both EU and UK business, families and individual litigants,” it says. “The optimum outcome for both sides will be an agreement reflecting our close existing relationship.”

However, the paper gives little indication how Britain intends to achieve this, as it will need to persuade the EU to preserve all the legal benefits of EU membership after the UK has left.

Officials concede that the major difference between their position paper and that of the EU is that Britain does not want to subject the new system to the direct authority of the European court of justice. In common with its ambitions for trade, the UK also wants to be able to negotiate separate and different arrangements with other non-EU countries.

Further details of how the UK intends to replace the role of the ECJ with a new international arbitration system are expected to be published on Wednesday.