The Liberal Democrats have vowed to vote against Article 50 unless a second referendum on the UK's Brexit deal from the EU is held.
Party leader Tim Farron branded the UK Government's handling of Britain's exit from the EU 'deeply worrying' and claimed that the country is moving towards a 'disasterous version of Brexit'.
Mr Farron said voters must be given a say on any Brexit agreement struck between the UK and Brussels, adding his party will not vote to trigger Article 50 unless a second referendum on the final deal is held.
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In a statement, he said: "Millions of people are deeply worried by the government's handling of Brexit.
"So my position is very clear: the Liberal Democrats believe that the people are sovereign.
"They must decide whether or not they agree with the deal that the government reaches with Brussels, which means a referendum at the end of the negotiations where people can either vote for the deal or to remain in Europe.
"We will vote against Article 50 unless it allows the people a vote on the deal, because the will of the people must prevail - both on departure and destination.
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"The government has no plan and their haphazard approach is leading us towards a disasterous version of Brexit which risks jobs, communities, security and the economic health of the nation."
Mr Farron's announcement came as several Labour and SDLP MPs, including shadow minister Catherine West, former Labour leadership contender Owen Smith and south London MP Helen Hayes, told the BBC that they were preparing to vote against triggering Article 50.
Last month the High Court ruled that the UK Government cannot trigger Article 50 and begin the UK's departure from the EU without giving MPs a vote on Brexit.
The Government will challenge the judges' ruling at the Supreme Court in December, arguing that prerogative powers could be used to trigger Article 50.
An outline of the grounds for appeal published by the Brexit Department said the High Court was mistaken and should have accepted "the Crown retains the power to give effect to the result of the EU referendum" by taking the "first step in the process" by notifying that it is triggering Article 50.
The Government's lawyers will argue that "in any event, the continued existence of the power to take that first step is clearly established and authorised by Parliament".
However, earlier this month the Scottish Government announced that it will lodge a formal application at the Supreme Court against the UK Government as it seeks to overturn the High Court's ruling that MPs must be given a vote before Article 50 can be triggered.
Read more: Blow for Nicola Sturgeon as Irish reject plea for direct talks over Brexit
The Government has said that it intends to stick to its current timetable, beginning the process of leaving the EU at the end of March.
Brexit Minister David Jones said: "Parliament voted by a margin of six to one to put the decision on whether to remain in, or leave, the EU in the hands of the British people.
"Now, because they didn't like the first answer, Liberal Democrat and Labour MPs seek to put the question all over again in hope of a different answer.
"They are attempting to thwart and reverse the decision that was taken on June 23.
"Only the Conservatives can be trusted to respect the outcome of the referendum and make a success of Brexit."
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