BREXIT battle lines have been drawn for a Downing Street showdown between Theresa May and Nicola Sturgeon next week after the First Minister insisted the prospect of a second Scottish independence referendum was “becoming ever clearer”.

Following a landmark Supreme Court ruling that MPs must vote on whether the government can start the Brexit process, Ms Sturgeon expressed disappointment that the justices had unanimously decided devolved parliaments did not warrant consultation.

In a statement, the First Minister said promises about embedding in law the Sewel Convention - whereby Westminster normally legislates on devolved matters with the consent of Holyrood - were “not worth the paper they were written on”.

Read more: UK Government expected to publish short and simple Article 50 Bill as early as Thursday

Declaring how the foundations of the devolution settlement were being shown to be “worthless,” Ms Sturgeon once again intensified the political rhetoric about a second independence referendum, saying the legal battle had thrown up fundamental issues above and beyond that of EU membership.

"It was becoming clearer by the day," she said "that Scotland's voice is simply not being heard or listened to within the UK."

And she added: “Is Scotland content for our future to be dictated by an increasingly right-wing Westminster Government with just one MP here or is it better that we take our future into our own hands? It is becoming ever clearer that this is a choice that Scotland must make.”

Ms Sturgeon has already insisted MSPs will have a vote on the triggering of Article 50.

It seems clear a majority will oppose the motion but this will not derail the UK Government from pressing ahead with its Brexit strategy and beginning the process of withdrawal by the end of March.

The fallout from the Supreme Court decision to uphold an earlier High Court judgement insisting the Prime Minister would have to allow MPs a vote on triggering Article 50 is likely to come to a head on Monday when the First Minister is expected to attend the Joint Ministerial Committee (JMC) in Downing Street chaired by Mrs May.

While Ms Sturgeon has ruled out a second Scottish independence referendum in 2017, some of her parliamentary colleagues are increasingly pointing to a second poll in 2018.

During exchanges in the House of Commons, Angus Brendan MacNeil, the SNP MP for the Western Isles, was blunt, saying: “As the UK Government pursues Brexit, Scotland must take the opportunity of an independence referendum.”

Pete Wishart, the Nationalists’ Shadow Commons Leader, warned that if the UK Government did not accept the “very reasonable proposals” being put to it by the Scottish Government, then “Scottish people are going to ask very quickly: what is the point of being here at all?”

Read more: UK Government expected to publish short and simple Article 50 Bill as early as Thursday

David Davis, the Brexit Secretary, who described himself as a “devolutionist,” insisted he had listened at great length to the Scottish Government’s arguments on Brexit, which include Scotland staying in the European single market, and while he agreed with some, he disagreed with others.

He stressed how through the JMC process the Scottish Government was being involved and told MPs: “I consider it incredibly important that in this process we protect…the interests of the people of Scotland.”

Mr Davis explained how the UK Government would now publish an Article 50 bill “within days” - possibly as early as Thursday - and which would be “as straightforward as possible”. He suggested the first Commons debate could come as early as next week.

With the bill due to be debated and voted on in the Commons and the Lords - where the Government does not have a majority - the Secretary of State warned MPs and peers “not to thwart the will of the people or frustrate or delay the process of exiting the European Union”.

Sir Keir Starmer, the Shadow Brexit Secretary, described the judges’ ruling as “a good day for democracy” but criticised the Government's court appeal as a "waste of time and money" as he accused the Prime Minister of trying to "sideline" Parliament in the run-up to the UK's divorce with Brussels.

Tom Brake for the Liberal Democrats said his party would put down an amendment to ensure there was a second referendum “on the terms of the UK’s future relationship with the European Union” ahead of Brexit.

But Secretary of State Mr Davis categorically ruled out such a prospect, saying he would not back another poll "under any circumstances". He told MPs that the arguments in favour of another referendum on the grounds that people did not know exactly what they were voting for last June were "patronising" and "undemocratic".

Read more: UK Government expected to publish short and simple Article 50 Bill as early as Thursday

Labour's Hilary Benn, who chairs the Commons Brexit Committee, was one of a number of MPs to call on Mr Davis to publish a White Paper, detailing the Government's Brexit objectives so they could be considered by MPs.

He added: "Because if the Government does not do so,'ll be showing a lack of respect for this House of Commons."

But Mr Davis insisted MPs would be kept "as well-informed" on Brexit as anything else of such importance. He also stressed how there would be many debates and votes at Westminster during the process, not least in relation to the Great Repeal Bill, which will end the EU’s legal supremacy in the UK by converting all EU requirements into British law as soon as the country leaves the Brussels bloc.

The Prime Minister can expect the overwhelming support of Tory MPs and Jeremy Corbyn has made clear Labour will not frustrate the process, although the Opposition will table amendments to ensure Britain maintains access to Europe's markets, workers' rights and environmental protection measures.

The SNP said it would be putting down some 50 amendments, including one that would ensure that if MPs voted down the final Brexit deal, there should be a “revision of the current terms of UK membership”; in other words, Britain would stay in the EU.

While the bill is set to get through, it could experience a rocky ride in the Commons; yet it could face its toughest opposition in the Lords.

Conservative backbencher Anne Main decried any attempt by peers to engage in parliamentary ping-pong and urged them not to “mess about” with the Article 50 legislation. “We must deliver what the British people have asked for,” she insisted.