The German government has warned Britain that there are still “leftovers” from the previous phase of Brexit negotiations that must be dealt with if Theresa May wants a final deal.

Though EU and British negotiators inked a joint text in December on Northern Ireland, the divorce bill, and citizens’ rights, the agreement merely embodied “sufficient progress” to move to the next phase of talks and left a variety of loose ends.

Peter Ptassek, Germany’s top diplomat in charge of Brexit said in a statement posted on social media that he had a “friendly reminder” for the UK negotiating team.

“‘Sufficient progress’ in withdrawal questions meant: we are not there yet. More work to be done,” he said.

“Many Brexit leftovers will surface when EU-Commission starts drafting withdrawal agreement, e.g. text on Ireland! Point here is: Legal text has to be clear.”

The statement was re-posted by Sabine Weyand, the European Commission’s deputy chief negotiator and the second in command after Michel Barnier – suggesting Brussels is on the same page as Berlin.

The UK side is now keen to move on to talks about the transition period, which will be starting within weeks, and the future trade framework, which the EU says can begin in March. The deadline for a full withdrawal agreement is October, Brussels says, to give EU institutions time to scrutinise and ratify the plan.

The intervention is a reminder that UK negotiators could be left fighting a rear-guard action on issues already deemed to be put to bed, while they also attempt to negotiate trade and transition.

Potential loose ends include the exact right EU and British citizens currently living abroad will have after Brexit – as well as exactly how the problem of the Northern Irish border will be resolved.

The initial draft mostly consisted of a guarantee from the UK to avoid a hard border with the Irish Republic rather than an actual negotiated solution for the province – though Britain did suggest it would keep rules aligned across the UK with the EU’s single market in the event of no other solution being found.

The EU’s negotiating team has however told member states it consisted this backstop to be incompatible with the UK’s stated policy of leaving the customs union and single market.

Brexit: the deciders Show all 8 1 /8 Brexit: the deciders Brexit: the deciders European Union's chief Brexit negotiator, Michel Barnier Getty Brexit: the deciders French President Emmanuel Macron Getty Brexit: the deciders German Chancellor Angela Merkel Reuters Brexit: the deciders Commission President Jean-Claude Juncker EPA Brexit: the deciders The European Parliament's chief Brexit negotiator Guy Verhofstadt Getty Brexit: the deciders Britain's Prime Minister Theresa May Getty Images Brexit: the deciders Britain's Chancellor of the Exchequer, Philip Hammond PA Brexit: the deciders After the first and second appointed Brexit secretaries resigned (David Davis and Dominic Raab respectively), Stephen Barclay is currently heading up the position PA

Additional scrutiny was put on the withdrawal agreement in December after David Davis provoked an outcry across the channel by suggesting the deal was a mere “statement of intent” rather than a legally binding document. This led the EU negotiators to demand it be converted into legal text as soon as possible and led to a protracted and potentially embarrassing public climb-down for the Brexit Secretary.