FORMER Conservative chancellor Ken Clarke is to vote with the SNP in a bid to block Theresa May from starting the official Brexit process.

On the first day of a two-day debate in the Commons, Mr Clarke described positive visions of a UK outside the European Union as a fantasy worthy of "wonderland" as he hit out at his own party accusing it of an anti-immigrant streak that would shock even Enoch Powell.

Mr Clarke's speech received a round of spontaneous applause from Labour and SNP MPs, breaching standard protocol within the Commons.

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The SNP amendment is being seen as a bid to kill off the Brexit Bill - which will be used to trigger Article 50 of the Lisbon Treaty and with it divorce talks with Brussels.

Former Deputy Prime Minister Nick Clegg also told MPs that they had a “duty” to vote against the Bill to force the Prime Minister to rethink her plans for a ‘hard’ Brexit.

Both attempts are expected to fail, however, after Labour declared that Mrs May should not be prevented from starting official exit negotiations.

The Tory Brexit Secretary David Davis told the Commons that they had to "trust the people" and the outcome of the EU referendum.

But earlier Theresa May had again moved to try to head off a rebellion on her own benches over the vote.

Sources suggested that a White Paper on Brexit would be published as early as Thursday.

This would allow time for it to be debated by MPs next week, a key demand of backbenchers.

It marks a dramatic turnaround as just two weeks ago Mrs May's position was that MPs would not get neither a vote nor a White Paper on Article 50.

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Labour also urged Mrs May to act unilaterally and guarantee EU nationals the right to stay after Brexit, before exit talks start.

But the shadow Brexit Secretary Keir Starmer admitted that the vote on the Brexit Bill was “difficult” for his party.

Labour is being torn apart by the issue, in part because the party represents some of the most pro- and anti-EU constituencies in the UK.

Party leader Jeremy Corbyn has imposed a three-line whip on his MPs, essentially ordering them to vote for the Bill.

But a number of MPs, including Scotland’s only Labour MP Ian Murray, are expected to rebel.

Frontbenchers including the former shadow Welsh secretary Jo Stevens have already resigned in order to vote against triggering exit talks.

Around 80 Labour MPs are thought to be preparing to defy their party leader.

A Labour frontbencher urged his colleagues to back the Bill to prevent a bigger Conservative majority at the next election.

Shadow Brexit minister Matthew Pennycook warned that Theresa May could be forced to call an early general election, in which, he predicted, she would win more seats.

But Labour MP Meg Hillier told the Commons that she could not "walk blindly through a lobby to give a trigger to a process without a shred of detail from the government".

On the government benches, pro-European Tory MP Anna Soubry said that she would vote for the Bill “with a heavy heart” in order to respect the result of the referendum.

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But Mr Clegg accused the Conservative Government of deliberately distorting the result of the referendum to suggest that that the public had voted for a 'hard' Brexit, in which control of UK borders is prioritised over access to the EU Single Market.

"The British people did not vote to make themselves poorer," he said.

SNP Europe spokesman Stephen Gethins urged other MPs to support his party's amendment, describing Brexit as "a backward and damaging step and it is an act of constitutional and economic sabotage".

Only one Scottish MP, Scottish Secretary David Mundell, is expected to vote to trigger Article 50.

Meanwhile, it emerged that Theresa May could hold more Brexit talks with Nicola Sturgeon before official negotiations with the EU begin.

Next week Mr Mundell is due to meet Scottish Brexit minister Michael Russell in London to discuss the Scottish Government's proposal for a separate deal for Scotland.