Last week senior EU officials accused the UK of “magical thinking over Brexit” and of attempting to use the Northern Irish Peace Process as a “bargaining chip” in the talks.
The comments drew a furious response from Britain, which accused the EU of failing to understand the “human cost” of the hard-won peace process.
Negotiators will also discuss EU citizens’ rights and the rights of British citizens in the EU after Brexit.
The EU insists that those rights must ultimately be guaranteed by the European Court of Justice, which the UK will not accept.
Today, campaign groups for expats in the UK and EU wrote to the EU-27, raising their fears over British plans to introduced a new “settled status” systems for EU migrants.
They also mentioned the Home Office’s erroneous sending of more than 100 letters warning EU citizens they faced detention in Britain, if they did not leave the country.
The Telegraph understands the gaffe will be brought up by EU negotiators this week.
A senior EU official said: “Our job is to protect EU citizens,” the senior official said, “Is it an issue of concern? Of course, it is. Is it relevant to the discussions? Yes.”