Dutch Prime Minister Mark Rutte warned British counterpart Theresa May on Friday that there could be "no tweaks" to the Brexit deal that the parliament in London rejected this week.
Rutte, one of several EU leaders who spoke by phone with May on Thursday and Friday, also said countries should "prepare for the worst" in the form of Britain crashing out with no deal.
"I said to her I really don't see how you can make further tweaks," Rutte told his weekly post-cabinet meeting press conference.
"There is nothing unreasonable in it (the deal). Not on the British side and not on the European side. That package is what it is, I'm afraid," Rutte said.
The plain-speaking Dutch premier was particularly firm on the so-called Irish backstop, a legal guarantee to keep the Irish border open whatever the outcome of negotiations on post-Brexit ties.
"Further tweaks on the backstop - like making it temporary or giving the British a one-side competency to halt the backstop... that's not going to fly," said Rutte.
Rutte said talk of Britain abandoning the result of the June 2016 Brexit referendum and staying in the European Union was "fantasyland".
"I am against Brexit, so of course I'm hoping for that. But it's not realistic and I'm not living in a fantasyland."
"There is nothing I can do that will prevent Brexit from taking place. The maximum influence I have... is to promote an orderly as possible Brexit."
Rutte advised Dutch companies to increase preparedness for a "really unwanted 'no deal' scenario."
"I’m advising companies to keep in mind all scenarios – to hope for the best and prepare for the worst," said Rutte, whose government will launch a major Brexit information campaign at the end of January.
May spoke to Rutte and German Chancellor Angela Merkel on Thursday night, and to EU leaders Jean-Claude Juncker and Donald Tusk by telephone Friday to discuss where to go next on Brexit.
She is expected to speak to more leaders over the weekend before laying a parliamentary motion for a new plan on Monday, her office said.
EU leaders have so far ruled out renegotiating the agreement, but have signalled they could postpone the withdrawal if May changes her "red lines" on leaving the EU's customs union and blocking free movement of citizens.