The House of Commons is deciding whether to reject changes made to the EU Withdrawal Bill by the House of Lords in a two-day debate taking place today and tomorrow.
He called for Brexit to be delayed, and for the public to get a second referendum on the terms of any exit deal.
The shock move came as the Prime Minister warned senior ministers in her Cabinet that defeat on a series of Lords amendments over the next two days would undermine the Government and make negotiations with Brussels harder.
The government won the first set of votes Tuesday, but looked set to face defeat on the issue of whether Parliament should have a "meaningful vote" on the Brexit deal.
The government will now enter talks with rebels about accepting a new amendment which would give MPs an effective veto on the Brexit deal May secures from the EU.
Five Labour MPs also rebelled by voting in favour of disagreeing with the Lords amendment: Ronnie Campbell, Frank Field, Kate Hoey, John Mann and Graham Stringer. This particular amendment-backed by "rebel" members of May's Conservative party and some opposition lawmakers-would give lawmakers a greater spread of choices.
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The opposition Labour Party wants to force the government to negotiate a Brexit deal where the United Kingdom retains "full access" to the EU's single market and that would ensure "no new impediments" to trade.
"I am trying to negotiate the best deal for Britain".
"Whatever we do, we're not going to reverse that", he said.
The meaningful vote is probably the most unsafe of the Lords amendments to the EU (Withdrawal) Bill - because it tees up an unpredictable vote on the final terms of Brexit, towards the end of this year, and opens up the possibility that MPs could demand that ministers change policy, in the event the terms were rejected by the House, or no deal was reached in the talks with the EU.... they could even demand (drumroll) a second referendum...
May says the changes would weaken the government's negotiating position, and the government will try to alter or reverse them in the House of Commons on Tuesday and Wednesday. It also attacked the unelected nature of the House of Lords (which traditionally scrutinizes laws passed to it by the elected lower chamber), linking it to a perceived attempt to frustrate the Brexit process. The Daily Express thundered: "Ignore the will of the people at your peril".
But the latest manoeuvre by a minority government that has been forced to compromise with parliament anxious some lawmakers who feared it would hand the European Union an incentive to withhold any agreement on an exit deal to force a softer Brexit.
"The people want us to leave the EU".