EU had said enough progress had been made to move talks on, but diplomats say much still to do.

The British government will be warned on Monday not to ignore the unfinished business of the EU divorce if it wants to secure a Brexit trade and transition deal.

Six weeks after EU leaders gave their blessing to moving the Brexit talks on to future arrangements, frustration is mounting that the UK is “not ready” to complete the divorce, which the EU deems essential for a deal before Britain’s departure on 29 March 2019.

In December the EU declared that London had made sufficient progress on the Brexit divorce issues of the Irish border, money and protecting citizens’ rights, but the government is perceived in Brussels to have made little advance since.

The Irish border issue is the most difficult hurdle, but negotiators must also resolve a host of technical matters, including Euratom, police cooperation and the role of the European court of justice.

European affairs ministers meeting in Brussels on Monday will issue a “gentle reminder” not to lose sight of these issues, one senior official told.

“The feeling here in Brussels is that the UK is pushing these on to the back burner and is now focusing more attention on the transition and the future,” the official said. “The message is don’t lose this out of sight, because we want to have it settled as well. And if we don’t have it settled this thing could go to the wire.”

British and EU negotiators held low-key talks in Brussels this month to discuss the issues, but progress was slow, according to several sources. One EU diplomat voiced frustration that the British side seemed “not ready” to advance on the topics: “They actually haven’t done much … We need to get cracking on the outstanding issues of which there are many.”

Germany’s Brexit envoy, Peter Ptassek, has said the final deal depends on resolving the withdrawal issues. “How fast can a deal be sealed? Depends exclusively on progress made in negotiations on legal text in Brussels. Energy needs to be focused here,” he tweeted last week.

The most thorny question is the future relationship with Ireland, a matter which is on a special negotiating track and is unlikely to be resolved soon. The EU will insist the UK uphold its promise to avoid a hard border, while ensuring the integrity of the European customs union and single market. The UK has always argued the Irish border issue is impossible to solve before trade talks, which have yet to start.

Beyond Ireland there is a long list of technical issues, many touching on the role of the European court of justice. The key issues are:

Brexit dispute settlement: “Significant divergences” remain on agreeing a process to resolve any future disputes about the Brexit deal, according to a European commission memo. The EU wants the European court to be the ultimate arbiter of any legal conflict related to the withdrawal deal. While the government has conceded a role for the ECJ on citizens’ rights, it wants to quit the court’s jurisdiction in all other areas.

Euratom: The two sides have agreed that countries would take charge of nuclear waste generated on their territories, but the UK’s future relationship with the nuclear body, which could involve the ECJ, is unresolved. Non-EU Switzerland is an “associate country” to Euratom, although 13 nations, such as the US and Japan, have looser cooperation agreements.

Unfinished court cases: The EU would like the ECJ to receive referrals of new court cases involving the UK after Brexit day, if the alleged rule-breaking happened during Britain’s membership. That does not square with the government’s red line that “the authority of EU law in Britain” will end on Brexit day.

Champagne and Parma ham: Brussels is demanding that the UK parliament draw up legislation before Brexit day to protect champagne, Parma ham, feta cheese and all food and wine bearing EU special status. Protecting regional produce is one of the EU’s top priorities in trade talks, but no discussions on this took place in the first phase of Brexit talks.

Goods in transit: The commission says “substantial work” remains to be done on sorting out the status of animal-derived products moving across the Brexit border, when the UK leaves the EU. The EU wants any dispute, for example, about adulterated cheese or mislabelled meat to be resolved under EU laws, but the UK insists the British authorities should take charge. A transition deal defers, rather than solves the problem.

Police cooperation: Both sides have said they want to complete procedures ongoing at the time of Brexit, but the UK has refused to sign up to EU procedural rules underpinned by the European court of justice.

British officials are confident these issues will be resolved. “We continue to engage in constructive technical discussions with the commission and look forward to moving on to the second phase of negotiations,” said a spokesperson at the Department for Exiting the European Union.

While their EU counterparts do not see them as deal-breakers, some think the British should be acting with more urgency.

“It is more complex than widely acknowledged … and I don’t know whether this is fully understood,” said one diplomat. “The sense of urgency on our side comes from the experience of negotiations until now, it always takes longer than foreseen.”

“The major problem will be to get the withdrawal agreement accepted and drafted by both sides,” said the Polish MEP Danuta Hübner, who chairs the European parliament’s constitutional affairs committee, which will vet the final Brexit deal.

Speaking to the Guardian, she said: “These [issues] were not making the front pages of the newspapers but they still have to be concluded.”