The UK has urged Brussels to show "respect" to expats by addressing "significant gaps" in their offer on their citizenship rights as it emerged that Britons in the European Union could lose their automatic ability to move to another country in the bloc after Brexit.
A British source close to the negotiations said the Brussels offer fell short of what the Government is offering EU nationals.
UK negotiators were surprised at the EU position on expats, who would not keep their automatic right under free movement rules to live in other countries in the bloc and would instead only be guaranteed the right to remain in the nation in which they are currently settled.
British expats will also lose existing rights to vote and stand in local elections under Brussels' proposals, while posted workers who are sent abroad from the UK to carry out a job on a temporary basis are not included in the EU offer.
By contrast, British officials highlighted offers to protect EU nationals' voting rights, offer those with strong ties to the UK a chance for longer breaks in residency, and remove comprehensive sickness insurance requirements.
The source said: "Overall, it has been a hugely productive week. UK-EU issue analysis of citizens' rights shows that after just three days' negotiations, we have reached agreement on 50% of all issues. This represents a significant step forward.
"But we still have doubts about the EU's plans and their commitment to upholding citizens' rights.
"The UK has put a serious offer on the table, but there are significant gaps in the EU's offer.
"The Commission and the member states now need to go away and discuss how they can bring their offer up to the level of the UK's.
"What we're offering EU citizens living in the UK is fair. We expect UK nationals living in the EU to be treated with the same respect ."
A senior EU official told a technical briefing in Brussels: "We would start from the assumption that in order to maintain the right of UK citizens to move around the EU27 this would require that the UK reciprocates this by allowing EU citizens to continue to move around freely, to also go to an EU member state and come back to the UK."