Jo Johnson's resignation as Theresa May tries to strike a Brexit deal tonight has sparked a call for other Tories to do the same.
The Orpington MP, brother of Boris Johnson, said that the emerging package - which the PM hopes to finalise within days - was a massive failure in British statecraft on the scale of Suez.
It comes as the DUP said it won't back Theresa May's apparent advocacy of a Northern Ireland backstop measure to avoid a hard border on Ireland.
If the DUP and Mrs May fail to agree, her government - which relies on the Northern Irish party for a majority - could collapse.
The Prime Minister has suffered an eye-watering 18 resignations since becoming PM in 2016 - although only a handful have been over Brexit.
Johnson said the 'reality' of what was being negotiated was far from what had been promised during the referendum campaign in 2016, and the country was faced with a 'terrible' choice between 'vassalage and chaos', adding: 'We are barreling towards an incoherent Brexit'.
Ex-Minister Philip Lee, who is among those who did quit over the EU process, urged other Tories to show the same 'courage' as Johnson.
'Following @JoJohnson's resignation I call upon my fellow MPs to show the same courage. We must allow our constituents to have a #FinalSay on Brexit. We must speak up now,' he said.