Theresa May has suffered a ministerial resignation ahead of crunch Commons votes on Brexit.
Remain-supporting Phillip Lee quit as justice minister, saying "if Brexit is worth doing, then it is certainly worth doing well" and it is "irresponsible to proceed as we are".
He said his main objection to Government policy was over the "wish to limit Parliament's role in contributing to the final outcome" - the so-called meaningful vote amendment.
His shock departure came as David Davis warned potential Tory rebels that they cannot undo the EU referendum, ahead of a tricky 48 hours in which the Government will try to get its Brexit programme back on track.
The Brexit Secretary spoke after some Conservatives signalled that they would support an amendment to the EU (Withdrawal Bill) tabled late on Monday by former attorney general Dominic Grieve giving more power to MPs.
The Commons begins two days of debate and votes on the Bill on Tuesday and Mr Grieve's amendment calls for a binding motion to be passed by the Commons, setting out how to proceed in the event of a "no deal" Brexit.
But Mr Davis told BBC Radio 4's Today programme: "A meaningful vote is not the ability to reverse the decision of the referendum.
"We will put in front of Parliament the decision for them to vote ... after that there will be a process of primary legislation to put the actual details of it in Parliament, so Parliament will actually decide on the application of the detail."
Asked what would happen if they voted against the deal, he said: "If they throw it out, well, they throw it out. We will have to go away, think about it and come back and make a statement, which is what I am saying to the House this afternoon."
The Prime Minister appeared to have defused a potentially explosive row over the EU customs union on Monday night as Tory pro-Europe rebels Sir Oliver Letwin and Nicky Morgan and Brexiteers Jacob Rees-Mogg and Sir Bill Cash came together to table a separate compromise amendment backing "a customs arrangement" with the EU.