WESTMINSTER should have a vote before the Brexit process begins to ensure the UK Government has a “clear plan” of action on how Britain will leave the European Union, Labour has insisted.

A letter setting out 170 questions – one for each day before Article 50 is triggered by March 31 next year – has been sent by the Labour leadership to David Davis, the Brexit secretary, ahead of a Commons debate on Wednesday when MPs will demand having a say before the formal process begins.

Sir Keir Starmer, Mr Davis’s Labour shadow, and his colleague Emily Thornberry, the shadow foreign secretary, say in the letter that a pre-talks vote is necessary to “ensure that, contrary to all public statements we have heard to date, the Government actually has a clear plan of what it is intending to achieve and that all members of the cabinet with responsibility in this area subscribe to that same plan".

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This is an allusion to the suggestion that unlike the “three Brexiteers” – Messrs Davis, Johnson and Fox – chancellor Philip Hammond, in particular, favours a soft or softer Brexit.

Sir Keir and Ms Thornberry add that if satisfactory answers to their catalogue of questions are not forthcoming, then it would reinforce the sense that the Conservative Government is “blundering into this process without a clear endgame in mind, repeating exactly the same mistake that the previous prime minister made with his ‘renegotiation’ of Britain’s EU membership last year; working to an artificial, self-imposed timetable with a flawed Plan A of what he wanted to achieve and no Plan B whatsoever”.

Earlier this week, Mr Davis set his face against MPs having a vote on the terms of the UK Government’s negotiating position, stressing how there would be no thwarting of the democratic wishes of the public as expressed in the EU referendum. There would, he insisted, be accountability to Parliament but no micro-management by it.

However, MPs from all parties, including the Conservative Party, are worried that Theresa May is intent on leading Britain to a so-called hard Brexit that would end the country’s membership of the European single market.

Their fears were underscored by the leaking of a Treasury document, which suggested that the UK could lose out to the tune of £66 billion a year if it left the single market.

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John McDonnell, the shadow chancellor, said: "Losing access to the single market would be devastating for jobs, livelihoods and our public services, yet the Tory Government are prepared to take this desperate step, despite being warned by their own experts of the consequences.”

His Labour colleague Dave Anderson said: “If the Tories are going to pursue this 'hard Brexit' option, they must make the consequences of this clear. Today, we still have no idea of the impact that this will have on Scottish economy, what it will mean for the rights of workers in Scotland, or the impact that it will have on the budget of the Scottish Parliament.

"It is time that the Government stops playing political games and begins to communicate exactly what this will mean for the people of Scotland," added the shadow Scottish secretary.

Tasmina Ahmed-Sheikh for the SNP said: “Everyone already knows that abandoning the single market would be bad news for business and the wider economy; what this Treasury report does is calculate the scale of the damage that would be done.

"It's little wonder that, by abandoning all economic reason, the Tories are running scared from any proper parliamentary scrutiny of their damaging plans," added the Nationalists’ spokeswoman on international trade.

Meantime, a report by Unite warned investment decisions on 15 new car models in the UK, including the Honda Civic and the Range Rover Sport, were "hanging by a thread" as the industry awaited the outcome of the Brexit negotiations.

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The trade union said hundreds of thousands of automotive and manufacturing jobs would be at risk unless the Prime Minister and her colleagues secured tariff-free access to the single market.

Elsewhere, the UK Government hailed the announcement that Britain and China had agreed to more than double the number of flights allowed to operate between the two countries.

It said the move would boost tourism and trade opportunities for the UK, “links, which will be vital as we look to build a confident, Global Britain after Brexit”.