A general election is the most democratic way of breaking the Brexit deadlock, Jeremy Corbyn is to argue.
The Labour leader will tell activists in Yorkshire that only a government with a « renewed mandate » will get public support for a withdrawal deal.
His party will oppose Theresa May’s deal next week, and push for a vote of no confidence if it is rejected by MPs.
The PM is considering trying to win over some Labour MPs to the deal by offering extra protection to workers.
Mrs May, who will host Japanese Prime Minister Shinzo Abe for talks at Downing Street on Thursday, is also continuing efforts to win over sceptical Conservative MPs ahead of Tuesday’s vote.
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However, Arlene Foster, leader of Northern Ireland’s DUP which has helped the government win votes since June 2017, has warned the PM her deal is « already dead ».
In a sign that the party has not been swayed by the government’s promise to give the Northern Ireland Assembly a veto over any new EU regulations introduced under the terms of the proposed backstop arrangement, she accused Mrs May of « wasting time ».
The government has lost two Brexit votes in two days. The first defeat limits the government’s financial powers in the event of a no-deal departure. The second forces the PM to announce new plans within three days if her deal fails in the Commons.
No 10 is now considering accepting an amendment tabled by Leave-supporting Labour backbencher John Mann that would provide for additional safeguards on workers rights and environmental protections.
« It will be seen as an attempt to win over some Labour waverers, » said BBC political correspondent Nick Eardley. « The Labour leadership, however, is unlikely to be swayed. »
Senior Conservatives have continued to express opposition to the withdrawal agreement and declaration on future relations, negotiated by Mrs May in November.
On the first of five days of debate on the deal, former international development secretary Andrew Mitchell said: « I’ve been astonished that she would bring back to the Commons a deal she knows she has absolutely no chance whatsoever to get through, and also with apparently no plan B. »
‘When not if’
In a speech on Thursday, Mr Corbyn will say that Mrs May – who abandoned a vote on the deal last month – will forfeit the right to govern if she cannot get her Brexit deal through the Commons.
« A government that cannot get its business through the Commons is no government at all, » he will say.
« To break the deadlock, an election is not only the most practical option, it is also the most democratic option. It would give the winning party a renewed mandate to negotiate a better deal for Britain and secure support for it in Parliament and across the country. »
Labour’s deputy leader Tom Watson told ITV’s Peston it was « a question of when not if » the party tabled a vote of no confidence in the government, although he suggested the opposition would wait to hear what Mrs May said in response to any defeat before deciding what to do.
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The DUP says it will support the government in any confidence vote if the Brexit deal is rejected, making a defeat less likely.
Critics of Mr Corbyn’s leadership say he is reluctant to go down this route because, if he fails, pressure will increase on him to endorse calls by many of his MPs – and what polls suggest is a majority of party members – for another referendum.
Former Conservative minister George Freeman accused Mr Corbyn of facing two ways at once, behaving like « a Brexiteer up north and a Remainer down south ».
Thursday’s Brexit debate will focus on agriculture and employment, with Environment Secretary Michael Gove and Business Secretary Greg Clark leading for the government.
Meanwhile, the Japanese prime minister is expected to use his visit to warn that a disorderly Brexit will be damaging for the 1,000 Japanese firms with operations in the UK, including Toyota and Honda.
Conservative and Labour MPs who voted this week to limit the government’s financial powers in the event of a « no-deal » Brexit have said Parliament is acting responsibly in trying to prevent this scenario. Many of them favour a closer, Norway-style relationship with Europe, or want to hold another referendum.
But Brexiteers have said the developments are meaningless as they do not oblige the government to do anything and the UK will still be leaving on 29 March.
Andrea Leadsom, the leader of the House of Commons, told ITV’s Peston on Wednesday it would be an « absolute betrayal » of the 17.4 million voters who backed Brexit, if the UK did not leave as planned.