Theresa May will tell European leaders directly that there will be no second referendum on Brexit when she addresses them for the first time in Brussels.
The Prime Minister will tell counterparts that the "priority now has got to be looking to the future" as she sets out Britain's position at a European summit.
But over dinner, she will insist that Britain does not want to damage the European Union when it quits the bloc.
No 10 said there had been suggestions in Europe that Britain would revisit the June 23 referendum decision so the PM will use the meetings to make it clear that it is "right and proper" that the result is "honoured".
"There has been a sense that there is still some debate in certain quarters of the European Union about whether that might be still a possibility and the Prime Minister has been absolutely clear many times that is not the case, but it is an opportunity for her to say that directly to all leaders precisely because we do need now to all be focusing on the future, which is the UK outside the European Union," a source said.
Mrs May will attempt to ease the jitters of other leaders who fear they will be harmed by Britain's exit from the bloc by vowing to deliver Britain's departure in the "best possible way", which means not just a good outcome for the UK but "how we can make it work for the EU too".
"She wants the outcome at the end of this process to be a strong Britain as a partner of a strong European Union," the source said.
"There has been some debate and concern expressed within the remaining member states about what does this mean for the future of the rest of the European Union.
"The Prime Minister will make clear she doesn't want the process of the UK leaving to be damaging for the rest of the European Union, that we want our departure to be a smooth, constructive, orderly process minimising uncertainty for countries, for people and our businesses and that we want to build a future partnership that cements Britain as a close, broad and deep partner for the EU."
The PM will also "reassure" other leaders that Britain will be a responsible EU member while it remains in the bloc.
Migration is the first formal item for the European Council meeting and Russia's bombing campaign in Syria will dominate discussions in the evening.
The PM will hold talks with Estonian prime minister Taavi Roivas and Romanian president Klaus Werner Iohannis in the margins of the summit.
Mrs May's visit to Brussels comes on the symbolic 100th day anniversary since she took office.