On Sunday the Brexit Secretary David Davis said guarantees on the Northern Ireland border were not legally binding unless the two sides reached a final deal.
A European Commission spokeswoman said the first-phase deal on the Northern Ireland border, the divorce bill and citizens’ rights did not strictly have the force of law.
“We see the joint report of Michel Barnier and David Davis as a deal between gentlemen and it is the clear understanding that it is fully backed and endorsed by the UK government.”
She added that “President Juncker had a meeting with Prime Minister May last Friday morning to ascertain that this is precisely the case. They shook hands.”
A clause inserted in Friday’s agreement at the insistence of the Republic of Ireland government says the UK would have full “regulatory alignment” with the EU in some areas if it leaves the EU without a deal.
She will tell MPs at a summit on Thursday that she expects EU leaders to agree to start talks about future trade and security and insist she did not cave in to Brussels over the so-called divorce bill and “alignment” with EU laws.
The UK is due to leave the EU in March 2019 but wants a two-year transition period after that date, with continued access to the single market to allow businesses to adjust.
That is expected to be the focus of the next round of talks in Brussels in the new year before discussions can start on a free trade agreement.