Labour is enduring a firestorm from all sides after most of its MPs backed Theresa May's plans to trigger Article 50 by the end of March if she revealed her strategy.
The party has been accused of handing the Conservatives a "blank cheque" for Brexit after 149 MPs, including leader Jeremy Corbyn, backed the motion. Labour MPs who didn't support the move were "named and shamed" via social media by the Conservative party for a lack of "respect" for the referendum vote.
On Tuesday, Theresa May agreed to publish details of her Brexit plan in an attempt to head off a backbench revolt over the motion. However she also added an amendment which challenged MPs to support her desired timetable for Brexit.
Former cabinet minister Iain Duncan Smith told Sky News this was a "historic moment".
He said: "They have had their bluff called, I suppose.
"They have had to vote to give us a date, so that is a real blank cheque for the Government.
"This means no matter what happens now in Parliament, Labour is signed up to the principle that by March 31 next year the Government will invoke Article 50."
The leader of the Liberal Democrats, Tim Farron, also weighed in on the debate.
He said: "Labour and the Tories are holding hands towards a hard Brexit.
"There should be democracy throughout this process, not a parliamentary stitch-up denying the public a say over the final deal.
"It's clear that only the Liberal Democrats are providing a real opposition to the Conservative Government and striving to keep Britain open, tolerant and united."
Shadow Brexit secretary Sir Keir Starmer denied this, telling Sky News: "If the plan the Government comes up with is a late, vague plan, they can expect further challenge.
"If they haven't produced one by the time we get the legislation, then it will be us who will put down amendments for the prerequisites of the plan."