The UK isn’t set up to defer Brexit past the current 31 October due date, Boris Johnson is to reveal to European Commission President Jean-Claude Juncker at chats on Monday.
The noon meeting in Luxembourg will be the first run through the pair have met since the PM got down to business in July.
A Downing Street source says Mr Johnson will pressure he needs to verify an arrangement by 18 October, after a key EU summit.
In any case, if unrealistic he will “dismiss any postponement offered” and leave with no arrangement.
The source said Mr Johnson “would clarify that he would not face any more deferrals”.
They included: “Any further expansion would be an immense misstep. It isn’t only an issue of the additional vacillate and deferral – it is likewise the extra long a very long time of enmity and division, and all at gigantic cost.”