The majority of MPs have voted to back Brexit and leave the EU by March 2019, in a symbolic vote that nonetheless represents an acceptance of the EU referendum result.
The House of Commons voted by 448 to 78 in favour of a symbolic proposal from Labour's Keir Starmer that calls on the government to provide extra details on the Brexit process from Downing Street before the UK begins the formal process of leaving the EU by invoking Article 50.
The Conservative government backed the Labour proposal in order to head off a rebellion by backbench Tory MPs.
However, as part of the compromise it amended the motion to added extra clauses requiring MPs to formally accept the result of the Brexit vote, to agree to the government’s proposed timetable on Brexit, and to accept that the publication of the Brexit plan will not undermine the government’s negotiating position.
As a result the vast majority of Labour and Conservative MPs are now on the record as formally backing Brexit before the next general election, although the motion is not binding.
Around 20 rebel Labour MPs, the SNP, the Lib Dems, and Green MP Caroline Lucas voted against the proposal, therefore formally registering their opposition to the Brexit process.
Starmer, Labour's shadow Brexit minister, had earlier warned Theresa May she had "no mandate" to take the UK out of the single market and demanded that the UK government publish a plan for leaving the EU.
Starmer insisted the move was not an attempt to "frustrate or delay" the triggering of Article 50 and said Labour will endeavour to "shape the debate" and use its influence to prevent Theresa May and the UK government from pursuing a so-called hard Brexit.
"I say this loud and clear – there is no mandate for hard Brexit, there is no consensus for hard Brexit," Starmer said. "In the last few months I’ve travelled across the UK … I know the secretary of state has been involved in the same exercise … the overwhelming evidence is that they do not want hard Brexit."
He added: "If we’re going to reach a consensus it must be a consensus that works for everybody. The ball is now in the government’s court to produce a timely plan which meets these requirements.
"That will be the start of the process, not the end. The start of scrutiny and accountability, not the end – and if the government fails to produce a timely and sufficiently detailed plan it should expect further challenge from this side."
The shadow Brexit secretary said Labour would only support the government's plan if it contained a statement on whether the UK would stay in the single market and the customs union. Starmer will also seek more assurances for Scotland, Wales, and Northern Ireland.
He conceded that the government cannot reveal everything about its objectives from the Brexit negotiations, saying there is "a level of detail, there are confidential issues, there are tactics which of course should not be disclosed", as doing so could risk undermining the discussions.
However, Starmer said publishing Brexit plan was necessary to allow the government's proposals to be subject to "the full and proper procedures" of the Westminster parliament, and warned that Labour will seek to "head off hard Brexit".
"The government must now prepare its plan and publish it," said Starmer. "I put the government on notice that if it fails to produce a plan by the time we are debating Article 50 legislation, ... amendments from this side and possibly from the other side of the house will be put forward."
In response, the Brexit secretary for the UK government, David Davis MP, said he "doesn't really know" what "hard Brexit" means, could not guarantee the government would reveal whether it intends to stay within the single market, and told Starmer there is a mandate to "leave the European Union, full stop".
"It's important that the house understands what we are aiming for, but it is also important we do not close off options before we absolutely have to," said Davis.
"Just this weekend, the leader of the opposition suggested he would seek to try to tie the hands of the government to certain outcomes, such as the particular status in terms of the European market. To do so would seriously undermine the national interest, because it undermines our ability to negotiate freely.
"As I said at my first appearance at this dispatch box in this role, parliament will be regularly updated and engaged. Keeping in mind these strategic aims – as well as the fact it cannot be in the national interest to reveal our position in detail – we will set out our strategic plans ahead of the triggering of Article 50."
He concluded: "We're happy to support the spirit of this motion, with the vital caveat that nothing we say will jeopardise our negotiating position."