In a dramatic Commons moment, MPs voted 294-293 in favour of a bid to require ministers to give fortnightly updates on the situation in Northern Ireland.
The plan, drawn up by former Tory attorney general Dominic Grieve, is designed to make it harder for the next Prime Minister to suspend Parliament to try and force Britain out of the EU without a deal.
Although several key elements of his proposal were either rejected by the Commons or not put to a vote, the amendment passed by the Commons could still complicate any attempt to “prorogue” Parliament.
Shadow Brexit Secretary Sir Keir Starmer said support for the amendment represented a “tight but important victory” that would make it “much harder” for the next Prime Minister to suspend Parliament.
The move came as Tory leadership frontrunner Boris Johnson again refused to rule out proroguing Parliament in a bid to ensure Brexit happens by 31 October.
In a televised head-to-head debate with rival Jeremy Hunt, Mr Johnson said: “I am not going to take anything off the table any more than I am going to take no-deal off the table, and I think it is absolutely bizarre at this stage in the negotiations for the UK yet again to be weakening its position.”
But Mr Hunt told ITV: “Well I think when that has happened in the past and Parliament was shut down against its will we actually had a civil war. And I think it would be a rather curious thing to do if this is about taking back control to Parliament, to actually shut it down. So my answer is no.”
Ahead of the knife-edge Commons vote, Mr Grieve dismissed talk of proroguing Parliament as “constitutionally improper”.
He told the BBC: “If you decide that Parliament is an inconvenience, when in fact it is the place where democratic legitimacy lies in our constitution and therefore it’s acceptable to get rid of it for a period because it might otherwise prevent you from doing something which Parliament would prevent, then it’s the end of democracy.”
The ex-attorney general had hoped to require ministers to come back to debate reports on Northern Ireland even if Parliament is closed, but that part of the plan was not selected for debate by Commons deputy speaker Eleanor Laing.
However, MPs did back a plan requiring ministers to produce the reports on power-sharing every two weeks from October until December – a period covering the crucial 31 October Brexit date.
Another amendment, calling on ministers to schedule debates on those reports, was rejected by 293 votes to 289.