THERESA May has signalled that MPs could be given the power to decide if the UK goes into the controversial Brexit backstop as she flagged up the alternative of extending the transition period.
The Prime Minister indicated it could be up to Parliament to make the choice with a so-called “parliamentary lock”.
The move appears to be a desperate attempt to try to reduce the number of Tory rebels, who are preparing to vote down her Brexit Plan next Tuesday; some estimates put the rebellion at more than 100.
The talking up of an extension to the transition period will worry Scottish Conservatives. 
Currently, the transition period sees the UK fishing industry comply with the rules of the EU’s hated Common Fisheries Policy until December 2020. An agreement on future arrangements has to be agreed with the EU27 by July of that year.
Mrs May as well as David Mundell have repeatedly said that the UK will become an independent coastal state on December 2020. 
Last month, remarks by the Scottish Secretary that at this date the industry’s compliance with the CFP would end were seized upon by fishermen’s representatives as confirmation that the UK would be out of the EU fishing regime at that point. 
However, Whitehall insiders were keen to stress Mr Mundell was stating “current policy” and was not referring to what might happen should the UK Government choose to extend the transition.
Last week, Mrs May wrote to Scottish Tory MPs restating how the UK would become an independent coastal state by December 2020 and noting how the future fisheries relationship with the EU27 had to be completed by the summer of that year.
However, the PM did not address the subject of the UK remaining in the CFP during any extended transition period. She told her colleagues: “I know and respect that your position, and that of the fishing industry, is that any situation that saw the UK in the CFP beyond 2020 would be unacceptable.” In her remarks, Mrs May clearly does not rule this option out. Any decision to maintain CFP compliance in an extended transition would cause uproar among Scottish Tories and could result in Mr Mundell resigning from the Cabinet.
Asked if the PM had a preference between the backstop and extending the transition period, her spokeswoman said: “She has always said the backstop is not something we want to use…There will be a choice ahead of the end of the implementation period for us to take.”
She explained that Mrs May was exploring with colleagues giving Parliament “a role” in making the decision between the UK going into the backstop and extending the transition period.
The key thing now is, ahead of Tuesday’s vote, is whether or not this “parliamentary lock” will satisfy some of her colleagues to limit the scale of the rebellion. 
Earlier, the PM told BBC Radio 4's Today programme: "There will be a choice between, if we get to that point, a choice between going into the backstop and extending the transition period. Now, there are pros and cons of both sides of that.
"People have a concern of the backstop, that we could be in it indefinitely. But, in the backstop we have no financial obligations, we have no free movement, we have very light level playing field rules with the EU.
"In the implementation period, we still have to negotiate the terms but there will be concerns about the fact that they would require, I'm sure they would require, some more money to be paid, for example. So there would be arguments on different sides."
Asked if she would be happy for Parliament to adjudicate on whether to go into the backstop or extend implementation, the PM said: "People are concerned about the role of the UK in making these decisions. And, the obvious, in terms of the UK, is for it to be Parliament that makes these decisions."
The backstop, intended to prevent the return of a hard border in Northern Ireland, is highly controversial as Brexiteer MPs claim it traps the UK into obeying rules set by Brussels without a say over them.
The Government insists it aims to conclude a comprehensive trade deal with the EU before a backstop arrangement would be needed.
Mrs May said that any deal with the EU such as a Canada-style free trade agreement favoured by some Brexiteers would also require a backstop arrangement.
Her comments came as the Democratic Unionist Party insisted it would withdraw support for her Government if the PM pressed ahead with the Brexit deal with the EU.
Asked if the DUP was prepared to precipitate a general election, the party's Brexit spokesman Sammy Wilson told Today: "If it comes to the point where the Government makes, shows, a determination to implement the Withdrawal Agreement with its damaging terms at present, or some future version of it, which is still equally damaging, we will not be supporting the Government."
Meanwhile, a European Court of Justice ruling on the reversibility of Article 50 will be announced just 24 hours before MPs vote on Mrs May's Brexit Plan.
In a tweet, the court said: "#Brexit: the ruling on the reversibility of #Article50 TEU (case C-621/18 Wightman) will be delivered on 10th December at 9 CET."
In Brussels, Michel Barnier again stressed the UK-EU agreement was the “only and the best possible”  deal on offer.
In a speech at the European Committee of the Regions, the EU’s chief negotiator described Brexit as a "lose-lose" situation and the deal was an exercise in "damage limitation".
On the issue of the Irish backstop, Mr Barnier explained: "It is a legally operational form of insurance that will ensure that we never see the return of a hard border, that we have north-south co-operation on the island of Ireland and that we protect the integrity of the single market.
"The backstop is not there in order to be used, necessarily. We will do our utmost to avoid ever having to use it."
In a message to MPs, he said politicians in Westminster and the European Parliament had to "take on the responsibility" as they considered the deal.
"The British Parliament will be voting on this in the next few days. This has serious implications for the future of the country. We respect democratic and parliamentary debate within the UK, just as we do within the European Parliament."
The EU chief negotiator, pointing out how a future trade deal with the UK would require ratification by national and regional parliaments across the EU, Mr Barnier added: "We are not at the end of the road. It's a long and arduous path."